Nonaqueous electrolytic solution and nonaqueous electrolyte battery

ABSTRACT

A nonaqueous electrolytic solution that can provide a battery that is low in gas generation, has a large capacity, and is excellent in storage characteristics and cycle characteristics. The solution contains an electrolyte, a nonaqueous solvent, and one or more compounds represented by Formulae (2) and (3):

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.13/397,197 filed Feb. 15, 2012 which is a Divisional of U.S. patentapplication Ser. No. 12/525,188 filed Jul. 30, 2009 which is a NationalStage of PCT/JP08/054,880 filed Mar. 17, 2008 and claims priority ofJapanese Patent Application No. 2007-070848 filed Mar. 19, 2007,Japanese Patent Application No. 2007-193525 filed Jul. 25, 2007 andJapanese Patent Application No. 2007-235600 filed Sep. 11, 2007, theentire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a nonaqueous electrolytic solution anda nonaqueous electrolyte battery using the same.

BACKGROUND OF THE INVENTION

Nonaqueous electrolyte batteries such as lithium secondary batterieshave been putting into practical use for various purposes, for example,from so-called household power sources for mobile phones, notebookcomputers, and so on to driving batteries equipped on vehicles such asautomobiles.

However, recent requirements for high-performance nonaqueous electrolytebatteries have become higher and higher, and battery characteristics aredesired to be improved.

In general, the electrolytic solution used in a nonaqueous electrolytebattery is mainly composed of an electrolyte and a nonaqueous solvent.As the main component of the nonaqueous solvent, for example, a cycliccarbonate such as ethylene carbonate or propylene carbonate, a chaincarbonate such as dimethyl carbonate, diethyl carbonate, or ethyl methylcarbonate, or a cyclic carboxylate such as γ-butyrolactone orγ-valerolactone is used.

In addition, in order to improve the battery characteristics, such asload characteristics, cycle characteristics, and storagecharacteristics, of these nonaqueous electrolyte batteries, variousinvestigations of nonaqueous solvents and electrolytes have beenperformed.

For example, Patent Document 1 proposes an electrolytic solutioncontaining a phosphinic ester for producing a battery in whichdegradation in battery performance during high-temperature storage issuppressed.

Patent Document 2 proposes an electrolytic solution containing aphosphonoacetate for producing a nonaqueous electrolyte secondarybattery that is safe because of its high flame retardancy and cangenerate a high voltage and also is excellent in charge and discharge.

Patent Document 3 proposes an electrolytic solution containing aphosphonoacetate for producing a battery excellent in flame retardancy.

Patent Document 4 proposes the use of a mixture of an asymmetric chaincarbonate and a cyclic carbonate having a double bond as a nonaqueoussolvent. By using this mixture, the cyclic carbonate having a doublebond preferentially reacts with a negative electrode to form ahigh-quality film on the surface of the negative electrode, and therebythe asymmetric chain carbonate is prevented from forming a nonconductivefilm on the surface of the negative electrode, resulting in enhancementsin storage characteristics and cycle characteristics.

However, recent requirements for high-performance batteries have becomehigher and higher, and it is required to achieve high capacity,high-temperature storage characteristics, and cycle characteristics athigh levels.

As a method of increasing the capacity, it has been investigated to fillthe restricted battery content with an active material in an amount aslarge as possible. In general, the active material layer of an electrodeis pressurized to increase the density, or a battery is designed suchthat the volume of materials other than the active material in thebattery is reduced as much as possible. However, when the activematerial layer of an electrode is pressurized to increase the density orthe amount of an electrolytic solution is decreased, the active materialcannot be uniformly used and degradation of the active material isaccelerated by uneven reaction. This tends to cause a problem in whichsufficient characteristics cannot be obtained. Furthermore, an increasein the capacity of a battery causes a decrease in the space inside thebattery. This also causes a problem in which the internal pressure ofthe battery is significantly increased even if the amount of gasgenerated by decomposition of the electrolytic solution is small.

In particular, in most cases using a nonaqueous electrolyte secondarybattery as a power supply in case of power outage or as a power supplyof portable equipment, the battery always supplies an extremely weakcurrent for compensating the self-discharge of the battery and is alwaysin a state of charging. In such a continuous charging state, theelectrode active material is always in a high activity state, and,simultaneously, heat generated by the equipment accelerates a decreasein the capacity of the battery or decomposition of the electrolyticsolution to tend to generate gas. In a battery that opens a relief valvewhen an abnormal increase in the internal pressure, due to abnormalitysuch as overcharge, is detected, the relief valve may be falsely openedif a large amount of gas is generated. In a battery not having a reliefvalve, the battery expands by the pressure of the generated gas, and thebattery itself may become disabled.

The nonaqueous electrolyte secondary battery including the electrolyticsolution described in Patent Document 1 is still unsatisfactory insuppression of gas generation, high-temperature storage characteristics,and cycle characteristics, as described above.

In the nonaqueous electrolyte secondary battery including theelectrolytic solution described in Patent Document 2 or 3, since thephosphonoacetate contained in the electrolytic solution has a hydrogenatom on the α-position of the carbonyl group, it is suggested thatelimination reaction of hydrogen tends to occur in reductivedecomposition on the negative electrode side. Thus, batterycharacteristics are still unsatisfactory.

The nonaqueous electrolyte secondary battery including the electrolyticsolution described in Patent Document 4 is also still unsatisfactory insuppression of the gas generation and high-temperature storagecharacteristics, as described above.

-   [Patent Document 1] Japanese Patent Publication 2004-363077A-   [Patent Document 2] Japanese Patent Publication H10-189039A-   [Patent Document 3] Japanese Patent Publication H11-233141A-   [Patent Document 4] Japanese Patent Publication H11-185806A

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a nonaqueouselectrolytic solution that can realize a nonaqueous electrolyte batterythat is low in gas generation, has a high capacity, and is excellent instorage characteristics and cycle characteristics, and to provide anonaqueous electrolyte battery including this nonaqueous electrolyticsolution.

The present inventors have conducted various investigations forachieving the above-mentioned object and, as a result, have found thatthe above-mentioned problems can be solved by adding a compound having aspecific structure to an electrolytic solution. Thus, the presentinvention has been accomplished.

A nonaqueous electrolytic solution of a first aspect of the presentinvention relates to a nonaqueous electrolytic solution containing anelectrolyte and a nonaqueous solvent dissolving the electrolyte, whereinthe nonaqueous electrolytic solution contains 0.001 vol % or more andless than 1 vol % of a compound represented by the following Formula (1)in the nonaqueous solvent.

In Formula (1), R¹ to R³ each independently represent an alkyl group of1 to 12 carbon atoms, which may be substituted by a halogen atom; and nrepresents an integer of 0 to 6.

A nonaqueous electrolytic solution of a second aspect of the presentinvention relates to a nonaqueous electrolytic solution containing anelectrolyte and a nonaqueous solvent dissolving the electrolyte, whereinthe nonaqueous electrolytic solution contains 0.001 vol % or more andless than 5 vol % of a compound represented by the following Formula (1)in the nonaqueous solvent and further contains at least one compoundselected from the group consisting of cyclic carbonate compounds havingcarbon-carbon unsaturated bonds, cyclic carbonate compounds havingfluorine atoms, monofluorophosphates, and difluorophosphates.

In Formula (1), R¹ to R³ each independently represent an alkyl group of1 to 12 carbon atoms, which may be substituted by a halogen atom; and nrepresents an integer of 0 to 6.

A nonaqueous electrolytic solution of a third aspect of the presentinvention relates to a nonaqueous electrolytic solution containing anelectrolyte and a nonaqueous solvent dissolving the electrolyte, whereinthe nonaqueous electrolytic solution contains a compound represented bythe following Formula (2) and/or a compound represented by the followingFormula (3).

In Formula (2), R¹¹ to R¹⁴ each independently represent a hydrogen atom,a halogen atom, or a monovalent substituent of 1 to 12 carbon atoms; R¹⁵represents an alkyl group of 1 to 12 carbon atoms, which may besubstituted by a halogen atom, an alkenyl group of 2 to 12 carbon atoms,which may be substituted by a halogen atom, an aryl group of 6 to 12carbon atoms, which may be substituted by a halogen atom, or an aralkylgroup of 7 to 12 carbon atoms, which may be substituted by a fluorineatom; and m represents an integer of 0 to 6.

hydrogen atom, a halogen atom, or a monovalent substituent of 1 to 12carbon atoms; R²⁵ represents an alkyl group of 1 to 12 carbon atoms,which may be substituted by a halogen atom, an alkenyl group of 2 to 12carbon atoms, which may be substituted by a halogen atom, an aryl groupof 6 to 12 carbon atoms, which may be substituted by a halogen atom, oran aralkyl group of 7 to 12 carbon atoms, which may be substituted by ahalogen atom; and r represents an integer of 0 to 6, wherein when bothR²¹ and R²² are alkoxy groups, r represents an integer of 1 to 6, and atleast one of R²³ and R²⁴ represent a group other than a hydrogen atom.

A nonaqueous electrolyte battery of a fourth aspect of the presentinvention relates to a nonaqueous electrolyte battery including anonaqueous electrolytic solution and negative and positive electrodesthat can absorb and desorb lithium ions, wherein the nonaqueouselectrolytic solution is the nonaqueous electrolytic solution accordingto any of the first to third aspects.

According to the present invention, a nonaqueous electrolyte batterythat is low in gas generation, has a high capacity, and is excellent instorage characteristics and cycle characteristics can be provided, andthe nonaqueous electrolyte battery can be reduced in size and can beenhanced in performance.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail below,but the following descriptions of elements are examples (typicalexamples) of the aspects of the present invention, and the presentinvention is not limited to these contents.

[Nonaqueous Electrolytic Solution]

The nonaqueous electrolytic solution of the present invention containsan electrolyte and a nonaqueous solvent dissolving the electrolyte, ingeneral, as main components, as in commonly used nonaqueous electrolyticsolutions.

{Electrolyte}

The electrolyte used is generally a lithium salt. Any lithium salt canbe used without particular limitation, as long as it is known to be usedfor this purpose. Specifically, the followings are exemplified.

Examples include inorganic lithium salts such as LiPF₆ and LiBF₄;fluorine-containing organic lithium salts such as LiCF₃SO₃,LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, lithium cyclic 1,2-perfluoroethanedisulfonyl imide, lithium cyclic 1,3-perfluoropropane disulfonyl imide,LiN(CF₃SO₂)(C₄F₉SO₂), LiC(CF₃SO₂)₃, LiPF₄(CF₃)₂, LiPF₄ (C₂F₅)₂, LiPF₄(CF₃SO₂)₂, LiPF₄(C₂F₅SO₂)₂, LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(CF₃SO₂)₂,and LiBF₂(C₂F₅SO₂)₂; and lithium bis(oxalate)borate and lithiumdifluoro(oxalate)borate.

Among them, LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂ and LiN(C₂F₅SO₂)₂ arepreferred from the viewpoint of the enhancement of battery performance,and LiPF₆ and LiBF₄ are particularly preferred.

These lithium salts may be used alone or in a combination of two ormore.

A preferred example of the combination of at least two lithium salts isa combination of LiPF₆ and LiBF₄, which has an effect to enhance thecycle characteristics. In this case, the ratio of LiBF₄ to the totalamount of the both is preferably 0.01 wt % or more and more preferably0.1 wt % or more and preferably 20 wt % or less and more preferably 5 wt% or less. When the ratio is less than this lower limit, a desiredeffect may be hardly obtained. When the ratio is higher than the upperlimit, the battery characteristics after high-temperature storage may bedeteriorated.

Another combination example is a combination of an inorganic lithiumsalt and a fluorine-containing organic lithium salt. In this case, theratio of the inorganic lithium salt to the total amount of the both isdesirably 70 wt % or more and 99 wt % or less. The fluorine-containinglithium salt in the combination is preferably LiN(CF₃SO₂)₂,LiN(C₂F₅SO₂)₂, lithium cyclic 1,2-perfluoroethane disulfonyl imide, orlithium cyclic 1,3-perfluoropropane disulfonyl imide. This combinationhas an effect of suppressing degradation due to high-temperaturestorage.

Furthermore, when the nonaqueous solvent contains 55 vol % or more ofγ-butyrolactone, the lithium salt is preferably a combination of LiBF₄or LiBF₄ and another lithium salt. In this case, the amount of LiBF₄ ispreferably 40 mol % or more to the total amount of the lithium salts.Particularly preferred are combinations of LiBF₄ at a ratio of 40 mol %or more and 95 mol % or less to the lithium salts and one or moreselected from the group consisting of LiPF₆, LiCF₃SO₃, LiN(CF₃SO₂)₂, andLiN(C₂F₅SO₂)₂ as the residue.

The concentration of these electrolytes in the nonaqueous electrolyticsolution is not particularly limited in order to exhibit the effect ofthe present invention, but is usually 0.5 mol/L or more, preferably 0.6mol/L or more, and more preferably 0.7 mol/L or more. The upper limitthereof is usually 3 mol/L or less, preferably 2 mol/L or less, morepreferably 1.8 mol/L or less, and most preferably 1.5 mol/L or less.When the concentration of the electrolyte is too low, the electricalconductivity of the electrolytic solution may be insufficient. On theother hand, when the concentration is too high, the electricalconductivity may be decreased due to an increase in viscosity, resultingin deterioration in battery performance.

{Nonaqueous Solvent}

The nonaqueous solvent can be adequately selected from those that areconventionally used as solvents of nonaqueous electrolytic solutions.Examples thereof include cyclic carbonates not having carbon-carbonunsaturated bonds, chain carbonates, cyclic ethers, chain ethers, cycliccarboxylates, chain carboxylates, sulfur-containing organic solvents,and phosphorus-containing organic solvents.

Examples of the cyclic carbonates not having carbon-carbon unsaturatedbonds include alkylene carbonates having an alkylene group of 2 to 4carbon atoms, such as ethylene carbonate, propylene carbonate, andbutylene carbonate. Among them, ethylene carbonate and propylenecarbonate are preferred from the viewpoint of enhancement of the batterycharacteristics, and ethylene carbonate is particularly preferred.

The chain carbonates are preferably dialkyl carbonates, and the numbersof the carbon atoms of the constituting alkyl groups are each preferablyone to five and more preferably one to four. Examples of the dialkylcarbonates include symmetric chain alkyl carbonates such as dimethylcarbonate, diethyl carbonate, and di-n-propyl carbonate; and asymmetricchain alkyl carbonates such as ethyl methyl carbonate, methyl-n-propylcarbonate, and ethyl-n-propyl carbonate. Among them, dimethyl carbonate,diethyl carbonate, and ethyl methyl carbonate are preferred from theviewpoint of enhancement of the battery characteristics (in particular,high-load discharge characteristics).

Examples of the cyclic ethers include tetrahydrofuran and2-methyltetrahydrofuran.

Examples of the chain ethers include dimethoxyethane anddimethoxymethane.

Examples of the cyclic carboxylates include γ-butyrolactone andγ-valerolactone.

Examples of the chain carboxylates include methyl acetate, methylpropionate, ethyl propionate, and methyl butyrate.

Examples of the sulfur-containing organic solvents include sulfolane,2-methylsulfolane, 3-methylsulfolane, and diethylsulfone.

Examples of the phosphorus-containing organic solvents include trimethylphosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethylphosphate, ethylene methyl phosphate, and ethylene ethyl phosphate.

These nonaqueous solvents may be used alone or in a combination of twoor more, but a combination of two or more compounds is preferred. Forexample, a combination of a high-dielectric solvent such as an alkylenecarbonate or a cyclic carboxylate and a low-viscosity solvent such as adialkyl carbonate or a chain carboxylate is preferred.

One preferred combination of the nonaqueous solvents is a combination ofan alkylene carbonate and a dialkyl carbonate as the main components. Insuch a combination, the total amount of the alkylene carbonate and thedialkyl carbonate in the nonaqueous solvent is 70 vol % or more,preferably 80 vol % or more, and more preferably 90 vol % or more; andthe ratio of the alkylene carbonate to the total amount of the alkylenecarbonate and the dialkyl carbonate is 5 vol % or more, preferably 10vol % or more, and more preferably 15 vol % or more and usually 50 vol %or less, preferably 35 vol % or less, more preferably 30 vol % or less,and most preferably 25 vol % or less. The use of such a combination ofthe nonaqueous solvents in a battery gives well-balanced cyclecharacteristics and high-temperature storage characteristics (inparticular, the remaining capacity after high-temperature storage andhigh-load discharge capacity) and is therefore preferred.

Examples of the preferred combination of an alkylene carbonate and adialkyl carbonate include combinations of ethylene carbonate anddimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylenecarbonate and ethyl methyl carbonate, ethylene carbonate and dimethylcarbonate and diethyl carbonate, ethylene carbonate and dimethylcarbonate and ethyl methyl carbonate, ethylene carbonate and diethylcarbonate and ethyl methyl carbonate, and ethylene carbonate anddimethyl carbonate and diethyl carbonate and ethyl methyl carbonate.

A combination in which propylene carbonate is further added to acombination of ethylene carbonate and a dialkyl carbonate is also apreferred example.

In the combination in which propylene carbonate is further added to acombination of ethylene carbonate and a dialkyl carbonate, the volumeratio of ethylene carbonate and propylene carbonate is preferably 99:1to 40:60 and more preferably 95:5 to 50:50. In addition, the ratio ofpropylene carbonate to the total amount of the nonaqueous solvent isusually 0.1 vol % or more, preferably 1 vol % or more, and morepreferably 2 vol % or more, and the upper limit thereof is usually 20vol % or less, preferably 8 vol % or less, and more preferably 5 vol %or less. The addition of propylene carbonate in this concentration rangefurther provides excellent low-temperature characteristics, whilemaintaining the characteristics of the combination of ethylene carbonateand a dialkyl carbonate, and is therefore preferred.

Among the combinations of ethylene carbonate and a dialkyl carbonate,those containing an asymmetric chain alkyl carbonate as the dialkylcarbonate are further preferred. In particular, those containingethylene carbonate and a symmetric chain alkyl carbonate and anasymmetric chain alkyl carbonate, such as ethylene carbonate anddimethyl carbonate and ethyl methyl carbonate, ethylene carbonate anddiethyl carbonate and ethyl methyl carbonate, and ethylene carbonate anddimethyl carbonate and diethyl carbonate and ethyl methyl carbonate,give well-balanced cycle characteristics and large-current dischargecharacteristics and are therefore preferred. Among them, the asymmetricchain alkyl carbonate is preferably ethyl methyl carbonate, and thealkyl group of the alkyl carbonate preferably has one or two carbonatoms.

In addition, in the case of the nonaqueous solvent containing diethylcarbonate, the gas generation in high-temperature storage is suppressedwhen the ratio of diethyl carbonate to the total amount of thenonaqueous solvent is usually 10 vol % or more, preferably 20 vol % ormore, more preferably 25 vol % or more, and most preferably 30 vol % ormore and the upper limit is usually 90 vol % or less, preferably 80 vol% or less, more preferably 75 vol % or less, and most preferably 70 vol% or less, and therefore such a range is preferred.

In addition, in the case of the nonaqueous solvent containing dimethylcarbonate, the load characteristics of the battery is enhanced when theratio of dimethyl carbonate to the total amount of the nonaqueoussolvent is usually 10 vol % or more, preferably 20 vol % or more, morepreferably 25 vol % or more, and most preferably 30 vol % or more andthe upper limit is usually 90 vol % or less, preferably 80 vol % orless, more preferably 75 vol % or less, and most preferably 70 vol % orless, and therefore such a range is preferred.

In addition, in the above-mentioned combinations including an alkylenecarbonate and a dialkyl carbonate as main components, another solventmay be further mixed therewith.

Other examples of the preferred nonaqueous solvent are those in whichone organic solvent selected from the group consisting of ethylenecarbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone ora solvent mixture composed of two or more organic solvents selected fromthe above-mentioned group is contained in a ratio of 60 vol % or more tothe total solvent amount. The nonaqueous electrolytic solutioncontaining this solvent mixture is low in evaporation and leak of thesolvent even if the electrolytic solution is used at high temperature.In particular, the cycle characteristics and the high-temperaturestorage characteristics are generally well-balanced by using acombination in which the total amount of ethylene carbonate andγ-butyrolactone based on the nonaqueous solvent is 70 vol % or more,preferably 80 vol % or more, and more preferably 90 vol % or more andthe volume ratio of the ethylene carbonate and the γ-butyrolactone is5:95 to 45:55 or a combination in which the total amount of ethylenecarbonate and propylene carbonate based on the nonaqueous solvent is 70vol % or more, preferably 80 vol % or more, and more preferably 90 vol %or more and the volume ratio of the ethylene carbonate and the propylenecarbonate is 30:70 to 60:40.

In this description, the volume of a nonaqueous solvent is a measuredvalue at 25° C., but in those, such as ethylene carbonate, that are asolid at 25° C., the measured value at the melting point is used.

{Compound Represented by Formula (1)}

The nonaqueous electrolytic solution according to the first or secondaspect of the present invention contains the above-described electrolyteand a nonaqueous solvent and is characterized in that the nonaqueoussolvent contains a compound (hereinafter, occasionally referred to as“Compound (1)”) represented by the following Formula (1).

In Formula (1), R¹ to R³ each independently represent an alkyl group of1 to 12 carbon atoms, which may be substituted by a halogen atom; and nrepresents an integer of 0 to 6.

In Formula (1) above, examples of the alkyl group of 1 to 12 carbonatoms of R¹ to R³ include linear, branched, or cyclic alkyl groups, suchas a methyl group, an ethyl group, a n-propyl group, an i-propyl group,a n-butyl group, an i-butyl group, a sec-butyl group, a tert-butylgroup, a pentyl group, a cyclopentyl group, and a cyclohexyl group. Thelower limit of the number of carbon atoms of each of R¹ to R³ is one ormore and preferably two or more, and the upper limit is 12 or less,preferably eight or less, and more preferably four or less.

Furthermore, the alkyl group may be substituted by a halogen atom suchas a fluorine atom. Examples of the group substituted by a fluorine atominclude partially fluorinated alkyl groups of the above-mentioned alkylgroups and perfluoroalkyl groups, such as a trifluoromethyl group, atrifluoroethyl group, and a pentafluoroethyl group.

Compounds (1) are exemplified below.

<Compound of n=0>

Trimethyl phosphonoformate, methyl diethyl phosphonoformate, methyldipropyl phosphonoformate, methyl dibutyl phosphonoformate, triethylphosphonoformate, ethyl dimethyl phosphonoformate, ethyl dipropylphosphonoformate, ethyl dibutyl phosphonoformate, tripropylphosphonoformate, propyl dimethyl phosphonoformate, propyl diethylphosphonoformate, propyl dibutyl phosphonoformate, tributylphosphonoformate, butyl dimethyl phosphonoformate, butyl diethylphosphonoformate, butyl dipropyl phosphonoformate, methylbis(2,2,2-trifluoroethyl)phosphonoformate, ethylbis(2,2,2-trifluoroethyl)phosphonoformate, propylbis(2,2,2-trifluoroethyl)phosphonoformate, butylbis(2,2,2-trifluoroethyl)phosphonoformate, and so on.

<Compound of n=1>

Trimethyl phosphonoacetate, methyl diethyl phosphonoacetate, methyldipropyl phosphonoacetate, methyl dibutyl phosphonoacetate, triethylphosphonoacetate, ethyl dimethyl phosphonoacetate, ethyl dipropylphosphonoacetate, ethyl dibutyl phosphonoacetate, tripropylphosphonoacetate, propyl dimethyl phosphonoacetate, propyl diethylphosphonoacetate, propyl dibutyl phosphonoacetate, tributylphosphonoacetate, butyl dimethyl phosphonoacetate, butyl diethylphosphonoacetate, butyl dipropyl phosphonoacetate, methylbis(2,2,2-trifluoroethyl)phosphonoacetate, ethylbis(2,2,2-trifluoroethyl)phosphonoacetate, propylbis(2,2,2-trifluoroethyl)phosphonoacetate, butylbis(2,2,2-trifluoroethyl)phosphonoacetate, and so on.

<Compound of n=2>

Trimethyl-3-phosphonopropionate, methyl diethyl-3-phosphonopropionate,methyl dipropyl-3-phosphonopropionate, methyl dibutyl3-phosphonopropionate, triethyl-3-phosphonopropionate, ethyldimethyl-3-phosphonopropionate, ethyl dipropyl-3-phosphonopropionate,ethyl dibutyl 3-phosphonopropionate, tripropyl-3-phosphonopropionate,propyl dimethyl-3-phosphonopropionate, propyldiethyl-3-phosphonopropionate, propyl dibutyl 3-phosphonopropionate,tributyl-3-phosphonopropionate, butyl dimethyl-3-phosphonopropionate,butyl diethyl-3-phosphonopropionate, butyldipropyl-3-phosphonopropionate, methylbis(2,2,2-trifluoroethyl)-3-phosphonopropionate, ethylbis(2,2,2-trifluoroethyl)-3-phosphonopropionate, propylbis(2,2,2-trifluoroethyl)-3-phosphonopropionate, butylbis(2,2,2-trifluoroethyl)-3-phosphonopropionate, and so on.

<Compound of n=3>

Trimethyl-4-phosphonobutyrate, methyl diethyl-4-phosphonobutyrate,methyl dipropyl-4-phosphonobutyrate, methyl dibutyl 4-phosphonobutyrate,triethyl-4-phosphonobutyrate, ethyl dimethyl-4-phosphonobutyrate, ethyldipropyl-4-phosphonobutyrate, ethyl dibutyl 4-phosphonobutyrate,tripropyl-4-phosphonobutyrate, propyl dimethyl-4-phosphonobutyrate,propyl diethyl-4-phosphonobutyrate, propyl dibutyl 4-phosphonobutyrate,tributyl-4-phosphonobutyrate, butyl dimethyl-4-phosphonobutyrate, butyldiethyl-4-phosphonobutyrate, butyl dipropyl-4-phosphonobutyrate, and soon.

Among them, from the viewpoint of enhancement of battery characteristicsafter high-temperature storage, compounds of n=0, 1, or 2 are preferred,and compounds of n=1 or 2 are particularly preferred.

Compounds (1) may be used alone or in a combination of two or more.

In the first aspect of the present invention, the nonaqueouselectrolytic solution does not contain at least one compound selectedfrom the group consisting of cyclic carbonate compounds havingcarbon-carbon unsaturated bonds, cyclic carbonate compounds havingfluorine atoms, monofluorophosphates, and difluorophosphates, which aredescribed below. The ratio of Compound (1) (when two or more Compounds(1) are used, the ratio of the sum of them) in the nonaqueouselectrolytic solution of the first aspect of the invention is usually0.001 vol % or more, preferably 0.05 vol % or more, more preferably 0.1vol % or more, and most preferably 0.2 vol % or more. In a lowerconcentration than the above, the effect of the present invention may behardly exhibited. On the other hand, if the concentration of Compound(1) is too high, the storage characteristics of the battery may bedeteriorated. Therefore, the upper limit is usually less than 1 vol %,preferably 0.8 vol % or less, and more preferably 0.7 vol % or less.

The nonaqueous electrolytic solution of the second aspect of the presentinvention contains, in addition to Compound (1), at least one compoundselected from the group consisting of cyclic carbonate compounds havingcarbon-carbon unsaturated bonds, cyclic carbonate compounds havingfluorine atoms, monofluorophosphates, and difluorophosphates. In thiscase, the ratio of Compound (1) in the nonaqueous solvent is usually0.001 vol % or more, preferably 0.05 vol % or more, more preferably 0.1vol % or more, and most preferably 0.2 vol % or more. In a lowerconcentration than the above, the effect of the present invention may behardly exhibited. On the other hand, if the concentration of Compound(1) is too high, the storage characteristics of the battery may bedeteriorated. Therefore, the upper limit is usually less than 5 vol %,preferably 3 vol % or less, more preferably 2 vol % or less, morepreferably 1 vol % or less, and most preferably 0.8 vol % or less.

When the nonaqueous electrolytic solution of the first or second aspectof the present invention is used, the amount of gas generated in anonaqueous electrolyte secondary battery is small, and the storagecharacteristics are excellent, though the reasons thereof are not clear.In addition, though the present invention is not limited to thefollowing action principle, it is thought that Compound (1) partiallyreacts with the positive electrode in a charged state to form a film,and this film suppresses side reaction between another electrolyticsolution component and an electrode active material even under ahigh-temperature atmosphere, as a result, the side reaction occurring inthe inside of the battery during high-temperature storage is suppressed,gas generation is suppressed, and the storage characteristics can beenhanced.

However, Compound (1) tends to be reductively decomposed on the negativeelectrode side. Therefore, the side reaction on the negative electrodeside increases with the amount of Compound (1), and the batterycharacteristics may be deteriorated. It is thought that when Compound(1) is used together with at least one compound selected from the groupconsisting of cyclic carbonate compounds having carbon-carbonunsaturated bonds, cyclic carbonate compounds having fluorine atoms,monofluorophosphates, and difluorophosphates, excessive reaction ofCompound (1) on the negative electrode side can be suppressed by a film,formed on the negative electrode, by the at least one compound selectedfrom the group consisting of cyclic carbonate compounds havingcarbon-carbon unsaturated bonds, cyclic carbonate compounds havingfluorine atoms, monofluorophosphates, and difluorophosphates.

{Compound Represented by Formula (2)/Compound Represented by Formula(3)}

The nonaqueous electrolytic solution of the third aspect of the presentinvention is characterized in that the nonaqueous electrolytic solutioncontains, in addition to the above-described electrolyte and nonaqueoussolvent, a compound (hereinafter, occasionally referred to as “Compound(2)”) represented by the following Formula (2) and/or a compound(hereinafter, occasionally referred to as “Compound (3)”) represented bythe following Formula (3).

In Formula (2), R¹¹ to R¹⁴ each independently represent a hydrogen atom,a halogen atom, or a monovalent substituent of 1 to 12 carbon atoms; R¹⁵represents an alkyl group of 1 to 12 carbon atoms, which may besubstituted by a halogen atom, an alkenyl group of 2 to 12 carbon atoms,which may be substituted by a halogen atom, an aryl group of 6 to 12carbon atoms, which may be substituted by a halogen atom, or an aralkylgroup of 7 to 12 carbon atoms, which may be substituted by a fluorineatom; and m represents an integer of 0 to 6.

In Formula (3), R²¹ to R²⁴ each independently represent a hydrogen atom,a halogen atom, or a monovalent substituent of 1 to 12 carbon atoms; R²⁵represents an alkyl group of 1 to 12 carbon atoms, which may besubstituted by a halogen atom, an alkenyl group of 2 to 12 carbon atoms,which may be substituted by a halogen atom, an aryl group of 6 to 12carbon atoms, which may be substituted by a halogen atom, or an aralkylgroup of 7 to 12 carbon atoms, which may be substituted by a halogenatom; and r represents an integer of 0 to 6, wherein when both R²¹ andR²² are alkoxy groups, r represents an integer of 1 to 6, and at leastone of R²³ and R²⁴ represent a group other than a hydrogen atom.

In Formula (2) above, the monovalent substituent of 1 to 12 carbon atomsin R¹¹ to R¹⁴ is not particularly limited as long as the effect of thepresent invention is not impaired, and examples thereof include an alkylgroup, an alkenyl group, an aryl group, an aralkyl group, an alkoxyalkylgroup, and groups represented by R^(a)—O— (R^(a) represents an alkylgroup, an alkenyl group, an aryl group, an aralkyl group, or analkoxyalkyl group, and hereinafter, occasionally referred to as “R^(a)Ogroup”).

In these monovalent substituent of 1 to 12 carbon atoms, a part of orall of the hydrogen atoms may be substituted by halogen atoms such asfluorine atoms. Among these monovalent substituents of 1 to 12 carbonatoms, the alkyl group and R^(a)O group are preferred.

In R^(a)O group in which R^(a) is an alkyl group, the alkyl group asR^(a) is preferably an alkyl group of 1 to 6 carbon atoms. Examples ofthe preferred alkyl group as R^(a) include a methyl group, an ethylgroup, a n-propyl group, and an i-propyl group. In particular, themethyl group and the ethyl group are preferred. In R^(a)O group in whichR^(a) is an aryl group, the aryl group as R^(a) is preferably a phenylgroup or a tolyl group, and the phenyl group is preferred.

In Formula (2), examples of the alkyl group of 1 to 12 carbon atoms asR¹⁵ include a methyl group, an ethyl group, a n-propyl group, ani-propyl group, a n-butyl group, an i-butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a cyclopentyl group, and a cyclohexylgroup. Preferable examples are chain (which may be linear or branched)or cyclic alkyl groups having preferably 1 to 6 carbon atoms and morepreferably 1 to 4 carbon atoms, and chain alkyl groups are preferred.

Examples of the alkenyl group of 2 to 12 carbon atoms as R¹⁵ include avinyl group and an allyl group, and those of 2 to 8 carbon atoms arepreferred, and those of 2 to 4 carbon atoms are particularly preferred.

Examples of the aryl group of 6 to 12 carbon atoms as R¹⁵ include aphenyl group, a tolyl group, and a xylyl group. Among them, the phenylgroup is preferred.

Examples of the aralkyl group of 7 to 12 carbon atoms as R¹⁵ include abenzyl group and a phenethyl group. Among them, the benzyl group ispreferred.

In addition, the above-mentioned alkyl group, alkenyl group, aryl group,and aralkyl group may be substituted by halogen atoms such as fluorineatoms, and examples of fluorinated groups include fluorinated alkylgroups such as a trifluoromethyl group, a trifluoroethyl group, and apentafluoroethyl group; fluorinated alkenyl groups such as a2-fluorovinyl group and a 3-fluoro-2-propenyl group; fluorinated arylgroups such as a 2-fluorophenyl group, a 3-fluorophenyl group, a4-fluorophenyl group, a 2,4-difluorophenyl group, and a3,5-difluorophenyl group; and fluorinated aralkyl groups such as a2-fluorobenzyl group, a 3-fluorobenzyl group, a 4-fluorobenzyl group, a2,4-difluorobenzyl group, and a 3,5-difluorobenzyl group.

m is an integer of 0 to 6, in particular, compounds of m=0 to 3 arepreferred, and compounds of m=0 to 2 are more preferred, and compoundsof m=0 or 1 are most preferred.

Compounds represented by Formula (2) are exemplified below.

<Examples of Compound of m=0>

Dimethyl acetylphosphonate, diethyl acetylphosphonate, dipropylacetylphosphonate, bis(trifluoromethyl)acetylphosphonate,bis(2,2,2-trifluoroethyl)acetylphosphonate,bis(pentafluoroethyl)acetylphosphonate, dially acetylphosphonate,diphenyl acetylphosphonate, dimethyl(trifluoroacetyl)phosphonate,diethyl(trifluoroacetyl)phosphonate,dipropyl(trifluoroacetyl)phosphonate, dimethyl(1-oxopropyl)phosphonate,diethyl(1-oxopropyl)phosphonate, dipropyl(1-oxopropyl)phosphonate,bis(trifluoromethyl)(1-oxopropyl)phosphonate,bis(2,2,2-trifluoroethyl)(1-oxopropyl)phosphonate,bis(pentafluoroethyl)(1-oxopropyl)phosphonate,diallyl(1-oxopropyl)phosphonate, diphenyl(1-oxopropyl)phosphonate,dimethyl(1-oxo-2-propenyl)phosphonate,diethyl(1-oxo-2-propenyl)phosphonate,dipropyl(1-oxo-2-propenyl)phosphonate, dimethyl(1-oxobutyl)phosphonate,diethyl(1-oxobutyl)phosphonate, dipropyl(1-oxobutyl)phosphonate,dimethyl(2-methyl-1-oxopropyl)phosphonate,diethyl(2-methyl-1-oxopropyl)phosphonate,dipropyl(2-methyl-1-oxopropyl)phosphonate,dimethyl(1-oxo-3-butenyl)phosphonate,diethyl(1-oxo-3-butenyl)phosphonate,dipropyl(1-oxo-3-butenyl)phosphonate,dimethyl(1-oxo-2-methoxyethyl)phosphonate,diethyl(1-oxo-2-methoxyethyl)phosphonate, dimethyl benzoylphosphonate,diethyl benzoylphosphonate, methyl acetyl methylphosphinate, methylethyl acetylphosphinate, methyl acetyl fluorophosphinate, methylmethyl(1-oxopropyl)phosphinate, methyl ethyl(1-oxopropyl)phosphinate,acetyl dimethylphosphine oxide, acetyl diethylphosphine oxide, acetyldifluorophosphine oxide, and so on.

<Examples of compound of m=1>

Dimethyl(2-oxopropyl)phosphonate, diethyl(2-oxopropyl)phosphonate,dipropyl(2-oxopropyl)phosphonate,bis(trifluoromethyl)(2-oxopropyl)phosphonate,bis(2,2,2-trifluoroethyl)(2-oxopropyl)phosphonate,bis(pentafluoroethyl)(2-oxopropyl)phosphonate,diallyl(2-oxopropyl)phosphonate, diphenyl(2-oxopropyl)phosphonate,dimethyl(2-oxobutyl)phosphonate, diethyl(2-oxobutyl)phosphonate,dipropyl(2-oxobutyl)phosphonate,dimethyl(1-methyl-2-oxopropyl)phosphonate,diethyl(1-methyl-2-oxopropyl)phosphonate,dimethyl(1-methoxy-2-oxopropyl)phosphonate,diethyl(1-methoxy-2-oxopropyl)phosphonate,dimethyl(1-fluoro-2-oxopropyl)phosphonate,diethyl(1-fluoro-2-oxopropyl)phosphonate, methylmethyl(2-oxopropyl)phosphinate, methyl ethyl(2-oxopropyl)phosphinate,methyl fluoro(2-oxopropyl)phosphinate, dimethyl(2-oxopropyl)phosphineoxide, diethyl(2-oxopropyl)phosphine oxide,difluoro(2-oxopropyl)phosphine oxide, and so on.

<Examples of Compound of m=2>

Dimethyl(3-oxobutyl)phosphonate, diethyl(3-oxobutyl)phosphonate,dipropyl(3-oxobutyl)phosphonate,bis(trifluoromethyl)(3-oxobutyl)phosphonate,bis(2,2,2-trifluoroethyl)(3-oxobutyl)phosphonate,bis(pentafluoroethyl)(3-oxobutyl)phosphonate,diallyl(3-oxobutyl)phosphonate, diphenyl(3-oxobutyl)phosphonate, and soon.

<Compound of m=3>

Dimethyl(4-oxopentyl)phosphonate, diethyl(4-oxopentyl)phosphonate,dipropyl(4-oxopentyl)phosphonate, and so on.

Among them, from the viewpoints of enhancement of batterycharacteristics after high-temperature storage and a cycle test,compounds of m=0, 1, or 2 are preferred, compounds of m=0 or 1 are morepreferred, and the following compounds are particularly preferred.

<Preferred Examples of Compound of m=0>

Dimethyl acetylphosphonate, diethyl acetylphosphonate, dipropylacetylphosphonate, bis(trifluoromethyl)acetylphosphonate,bis(2,2,2-trifluoroethyl)acetylphosphonate,bis(pentafluoroethyl)acetylphosphonate,dimethyl(trifluoroacetyl)phosphonate,diethyl(trifluoroacetyl)phosphonate,dipropyl(trifluoroacetyl)phosphonate, dimethyl(1-oxopropyl)phosphonate,diethyl(1-oxopropyl)phosphonate, dipropyl(1-oxopropyl)phosphonate,bis(trifluoromethyl)(1-oxopropyl)phosphonate,bis(2,2,2-trifluoroethyl)(1-oxopropyl)phosphonate,bis(pentafluoroethyl)(1-oxopropyl)phosphonate,dimethyl(1-oxobutyl)phosphonate, diethyl(1-oxobutyl)phosphonate,dipropyl(1-oxobutyl)phosphonate,dimethyl(2-methyl-1-oxopropyl)phosphonate,diethyl(2-methyl-1-oxopropyl)phosphonate,dipropyl(2-methyl-1-oxopropyl)phosphonate, and so on.

<Preferred Examples of Compound of m=1>

Dimethyl(2-oxopropyl)phosphonate, diethyl(2-oxopropyl)phosphonate,dipropyl(2-oxopropyl)phosphonate,bis(trifluoromethyl)(2-oxopropyl)phosphonate,bis(2,2,2-trifluoroethyl)(2-oxopropyl)phosphonate,bis(pentafluoroethyl)(2-oxopropyl)phosphonate,dimethyl(2-oxobutyl)phosphonate, diethyl(2-oxobutyl)phosphonate,dipropyl(2-oxobutyl)phosphonate, and so on.

The compounds represented by Formula (2) may be used alone or in acombination of two or more.

In Formula (3) above, the monovalent substituent of 1 to 12 carbon atomsin R²¹ to R²⁴ is not particularly limited as long as the effect of thepresent invention is not impaired, and examples thereof include an alkylgroup, an alkenyl group, an aryl group, an aralkyl group, an alkoxyalkylgroup, and groups represented by R^(b)—O— (R^(b) represents an alkylgroup, an alkenyl group, an aryl group, an aralkyl group, or analkoxyalkyl group, and hereinafter, occasionally referred to as “R^(b)Ogroup”).

In these monovalent substituent of 1 to 12 carbon atoms, a part of orall of the hydrogen atoms may be substituted by halogen atoms such asfluorine atoms.

Among these monovalent substituents of 1 to 12 carbon atoms, from theviewpoint of enhancement of battery characteristics, R²¹ and R²² arepreferably groups that are selected from alkyl groups, alkenyl groups,aryl groups, and R^(b)O groups and more preferably substituents that areselected from alkyl groups, alkenyl groups, and R^(b)O groups.

In addition, R²³ and R²⁴ are preferably groups that are selected fromalkyl groups, alkenyl groups, aryl groups, and R^(b)O groups and morepreferably substituents that are selected from alkyl groups, alkenylgroups, and R^(b)O groups.

In Formula (3), examples of the alkyl group of 1 to 12 carbon atoms asR²⁵ include a methyl group, an ethyl group, a n-propyl group, ani-propyl group, a n-butyl group, an i-butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a cyclopentyl group, and a cyclohexylgroup. Preferable examples are chain (which may be linear or branched)or cyclic alkyl groups having preferably 1 to 6 carbon atoms and morepreferably 1 to 4 carbon atoms, and chain alkyl groups are preferred.

Examples of the alkenyl group of 2 to 12 carbon atoms as R²⁵ include avinyl group and an allyl group, and those of 2 to 8 carbon atoms arepreferred, and those of 2 to 4 carbon atoms are particularly preferred.

Examples of the aryl group of 6 to 12 carbon atoms as R²⁵ include aphenyl group, a tolyl group, and a xylyl group. Among them, the phenylgroup is preferred.

Examples of the aralkyl group of 7 to 12 carbon atoms as R²⁵ include abenzyl group and a phenethyl group. Among them, the benzyl group ispreferred.

In addition, the above-mentioned alkyl group, alkenyl group, aryl group,and aralkyl group may be substituted by halogen atoms such as fluorineatoms, and examples of fluorinated groups include fluorinated alkylgroups such as a trifluoromethyl group, a trifluoroethyl group, and apentafluoroethyl group; fluorinated alkenyl groups such as a2-fluorovinyl group and a 3-fluoro-2-propenyl group; fluorinated arylgroups such as a 2-fluorophenyl group, a 3-fluorophenyl group, a4-fluorophenyl group, a 2,4-difluorophenyl group, and a3,5-difluorophenyl group; and fluorinated aralkyl groups such as a2-fluorobenzyl group, a 3-fluorobenzyl group, a 4-fluorobenzyl group, a2,4-difluorobenzyl group, and a 3,5-difluorobenzyl group.

r is an integer of 0 to 6, in particular, compounds of r=0 to 3 arepreferred, and compounds of r=0 to 2 are more preferred, and compoundsof r=0 or 1 are most preferred.

In addition, in Formula (3), when both R²¹ and R²² are alkoxy groups, rrepresents an integer of 1 to 6, and at least one of R²³ and R²⁴ isother than a hydrogen atom. Compounds in which both R²¹ and R²² arealkoxy groups and r=0 tend to be reductively decomposed on the negativeelectrode side, and, therefore, the battery characteristics may beinsufficient compared to the case of compounds in which r represents aninteger of 1 to 6 and at least one of R²³ and R²⁴ is other than ahydrogen atom. Furthermore, it is assumed that even if r represents aninteger of 1 or higher, when both R²³ and R²⁴ are hydrogen atoms,elimination reaction of hydrogen tends to occur during reductivedecomposition on the negative electrode side. Therefore, the batterycharacteristics may be insufficient compared to the case of compounds inwhich at least one of R²³ and R²⁴ is other than a hydrogen atom.

Compounds represented by Formula (3) are exemplified below.

<Compound of r=0>

Methyl(dimethylphosphinyl)formate, methyl(diethylphosphinyl)formate,methyl(dipropylphosphinyl)formate, methyl[bis(trifluoromethyl)phosphinyl]formate, methyl[bis(2,2,2-trifluoroethyl)phosphinyl]formate,ethyl(dimethylphosphinyl)formate, ethyl(diethylphosphinyl)formate,ethyl(dipropylphosphinyl)formate,ethyl[bis(trifluoromethyl)phosphinyl]formate,ethyl[bis(2,2,2-trifluoroethyl)phosphinyl]formate,methyl(difluorophosphinyl)formate, ethyl(difluorophosphinyl)formate,methyl(methoxymethylphosphinyl)formate,methyl(ethoxyethylphosphinyl)formate,ethyl(methoxymethylphosphinyl)formate,ethyl(ethoxyethylphosphinyl)formate,methyl(methoxyfluorophosphinyl)formate,ethyl(ethoxyfluorophosphinyl)formate, and so on.

<Compound of r=1>

Methyl(dimethylphosphinyl)acetate, methyl(diethylphosphinyl)acetate,methyl(dipropylphosphinyl)acetate,methyl[bis(trifluoromethyl)phosphinyl]acetate,methyl[bis(2,2,2-trifluoroethyl)phosphinyl]acetate,ethyl(dimethylphosphinyl)acetate, ethyl(diethylphosphinyl)acetate,ethyl(dipropylphosphinyl)acetate,ethyl[bis(trifluoromethyl)phosphinyl]acetate,ethyl[bis(2,2,2-trifluoroethyl)phosphinyl]acetate,methyl(dimethylphosphinyl)fluoroacetate,methyl(diethylphosphinyl)fluoroacetate,ethyl(dimethylphosphinyl)fluoroacetate,ethyl(diethylphosphinyl)fluoroacetate,methyl-2-(dimethylphosphinyl)propionate,methyl-2-(diethylphosphinyl)propionate,ethyl-2-(dimethylphosphinyl)propionate,ethyl-2-(diethylphosphinyl)propionate,methyl-2-(dimethylphosphinyl)butyrate,methyl-2-(diethylphosphinyl)butyrate,ethyl-2-(dimethylphosphinyl)butyrate,ethyl-2-(diethylphosphinyl)butyrate, methyl(difluorophosphinyl)acetate,ethyl(difluorophosphinyl)acetate,methyl(methoxymethylphosphinyl)acetate,methyl(ethoxyethylphosphinyl)acetate,ethyl(methoxymethylphosphinyl)acetate,ethyl(ethoxyethylphosphinyl)acetate,methyl(methoxyfluorophosphinyl)acetate,ethyl(ethoxyfluorophosphinyl)acetate, trimethyl phosphonofluoroacetate,methyl(diethylphosphono)fluoroacetate, triethyl phosphonofluoroacetate,trimethyl-2-phosphonopropionate, methyl-2-diethylphosphonopropionate,triethyl-2-phosphonopropionate, ethyl-2-dimethyl phosphonopropionate,methyl-2-[bis(2,2,2-trifluoroethyl)phosphono]propionate,ethyl-2-[bis(2,2,2-trifluoroethyl)phosphono]propionate,trimethyl-2-phosphonobutyrate, methyl-2-diethyl phosphonobutyrate,triethyl-2-phosphonobutyrate, ethyl-2-dimethyl phosphonobutyrate, and soon.

<Compound of r=2>

Methyl-3-(dimethylphosphinyl)propionate,methyl-3-(diethylphosphinyl)propionate,ethyl-3-(dimethylphosphinyl)propionate,ethyl-3-(diethylphosphinyl)propionate,methyl-3-(dimethylphosphinyl)butyrate,methyl-3-(diethylphosphinyl)butyrate,ethyl-3-(dimethylphosphinyl)butyrate,ethyl-3-(diethylphosphinyl)butyrate,methyl-3-(methoxymethylphosphinyl)propionate,methyl-3-(ethoxyethylphosphinyl)propionate,ethyl-3-(methoxymethylphosphinyl)propionate,ethyl-3-(ethoxyethylphosphinyl)propionate, and so on.

Among them, from the viewpoints of enhancement of batterycharacteristics after high-temperature storage and a cycle test,compounds of r=0 or 1 are particularly preferred, and, above all, thefollowing compounds are preferred.

<Preferred examples of compound of r=0>

Methyl(dimethylphosphinyl)formate, methyl(diethylphosphinyl)formate,ethyl(dimethylphosphinyl)formate, ethyl (diethylphosphinyl)formate,methyl(difluorophosphinyl)formate, ethyl(difluorophosphinyl)formate,methyl(methoxymethylphosphinyl)formate,methyl(ethoxyethylphosphinyl)formate,ethyl(methoxymethylphosphinyl)formate,ethyl(ethoxyethylphosphinyl)formate,methyl(methoxyfluorophosphinyl)formate,ethyl(ethoxyfluorophosphinyl)formate, and so on.

<Preferred examples of compound of r=1>

Methyl(dimethylphosphinyl)acetate, methyl(diethylphosphinyl)acetate,ethyl(dimethylphosphinyl)acetate, ethyl(diethylphosphinyl)acetate,methyl(dimethylphosphinyl)fluoroacetate,methyl(diethylphosphinyl)fluoroacetate,ethyl(dimethylphosphinyl)fluoroacetate,ethyl(diethylphosphinyl)fluoroacetate,methyl-2-(dimethylphosphinyl)propionate,methyl-2-(diethylphosphinyl)propionate,ethyl-2-(dimethylphosphinyl)propionate,ethyl-2-(diethylphosphinyl)propionate,methyl-2-(dimethylphosphinyl)butyrate,methyl-2-(diethylphosphinyl)butyrate,ethyl-2-(dimethylphosphinyl)butyrate,ethyl-2-(diethylphosphinyl)butyrate, methyl(difluorophosphinyl)acetate,ethyl(difluorophosphinyl)acetate,methyl(methoxymethylphosphinyl)acetate,methyl(ethoxyethylphosphinyl)acetate,ethyl(methoxymethylphosphinyl)acetate,ethyl(ethoxyethylphosphinyl)acetate,methyl(methoxyflucrophosphinyl)acetate,ethyl(ethoxyfluorophosphinyl)acetate, trimethyl phosphonofluoroacetate,methyl(diethylphosphono)fluoroacetate, triethyl phosphonofluoroacetate,trimethyl-2-phosphonopropionate, methyl-2-diethylphosphonopropionate,triethyl-2-phosphonopropionate, ethyl-2-dimethyl phosphonopropionate,trimethyl-2-phosphonobutyrate, methyl-2-diethyl phosphonobutyrate,triethyl-2-phosphonobutyrate, ethyl-2-dimethyl phosphonobutyrate, and soon.

The compounds represented by Formula (3) may be used alone or in acombination of two or more.

The ratio of the compound represented by Compound (2) and/or Compound(3) in the nonaqueous electrolytic solution of the third aspect of thepresent invention (when two or more compounds are used, the ratio of thesum of them) is usually 0.001 wt % or more, preferably 0.01 wt % ormore, more preferably 0.05 wt % or more, and most preferably 0.1 wt % ormore. In a lower concentration than the above, the effect of the presentinvention may be hardly exhibited. On the other hand, if theconcentration is too high, the capacity of the battery may be decreased.Therefore, the upper limit is usually 10 wt % or less, preferably 4 wt %or less, more preferably 2 wt % or less, more preferably 1 wt % or less,and most preferably 0.8 wt % or less.

When the nonaqueous electrolytic solution containing Compound (2) and/orCompound (3) according to the present invention is used, the amount ofgas generated in a nonaqueous electrolyte secondary battery is small,and the storage characteristics are excellent, though the reasonsthereof are not clear. In addition, though the present invention is notlimited to the following action principle, it is thought that Compound(3) partially reacts with the positive electrode in a charged state orcoordinates on the surface of the positive electrode to suppress sidereaction between another electrolytic solution component and anelectrode active material, as a result, the side reaction occurring inthe inside of the battery during high-temperature storage anddegradation of the positive electrode are suppressed, resulting insuppression of gas generation and enhancement of storagecharacteristics. Furthermore, it is thought that in a compound having asubstituent other than hydrogen on the α-position of carbonyl, the gasgeneration is further suppressed by suppressing the elimination reactionof hydrogen in reductive decomposition on the negative electrode side.

In addition, it is thought that Compound (2) partially reacts with thepositive electrode in a charged state to form a film, and this filmsuppresses side reaction between another electrolytic solution componentand an electrode active material even under a high-temperatureatmosphere, as a result, the side reaction occurring in the inside ofthe battery during high-temperature storage and degradation of thepositive electrode are suppressed, resulting in suppression of gasgeneration and enhancement of storage characteristics. It is thoughtthat, in particular, since Compound (2) has a PO bond and a CO bond, theability of protecting the surface of the positive electrode (bycoordination or formation of a protection film) is high, compared to thecase of phosphinic ester, and therefore the side reaction between thepositive electrode and the electrolytic solution is suppressed, and abattery that is low in gas generation and excellent in batterycharacteristics can be provided.

{Other Compounds}

The nonaqueous electrolytic solution according to the first to thirdaspect of the present invention may contain a cyclic carbonate compoundhaving a carbon-carbon unsaturated bond, a cyclic carbonate compoundhaving a fluorine atom, a monofluorophosphate, a difluorophosphate, orother various compounds, such as a conventionally known overchargeprotection agent, as auxiliaries.

<Cyclic Carbonate Compound Having Carbon-Carbon Unsaturated Bond>

The cyclic carbonate compound having a carbon-carbon unsaturated bondforms a stable protection film on the surface of a negative electrodeand can thereby enhance the cycle characteristics of the battery.

Examples of the cyclic carbonate compound having a carbon-carbonunsaturated bond include vinylene carbonate compounds such as vinylenecarbonate, methyl vinylene carbonate, ethyl vinylene carbonate,4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate,fluorovinylene carbonate, and trifluoromethyl vinylene carbonate; vinylethylene carbonate compounds such as vinyl ethylene carbonate,4-methyl-4-vinyl ethylene carbonate, 4-ethyl-4-vinyl ethylene carbonate,4-n-propyl-4-vinyl ethylene carbonate, 5-methyl-4-vinyl ethylenecarbonate, 4,4-divinyl ethylene carbonate, and 4,5-divinyl ethylenecarbonate; and methylene ethylene carbonate compounds such as4,4-dimethyl-5-methylene ethylene carbonate and 4,4-diethyl-5-methyleneethylene carbonate. Among them, vinylene carbonate, vinyl ethylenecarbonate, 4-methyl-4-vinyl ethylene carbonate, and 4,5-divinyl ethylenecarbonate are preferred from the viewpoint of enhancement of cyclecharacteristics. In particular, vinylene carbonate and vinyl ethylenecarbonate are more preferred, and vinylene carbonate is most preferred.

These cyclic carbonate compounds having carbon-carbon unsaturated bondsmay be used alone or in a combination of two or more. When a combinationof two or more cyclic carbonate compounds having carbon-carbonunsaturated bonds is used, a combination of vinylene carbonate and vinylethylene carbonate is preferred.

When the nonaqueous electrolytic solution contains the cyclic carbonatecompound having a carbon-carbon unsaturated bond, the ratio thereof inthe nonaqueous electrolytic solution is usually 0.01 wt % or more,preferably 0.1 wt % or more, more preferably 0.3 wt % or more, and mostpreferably 0.5 wt % or more. When the amount of the cyclic carbonatecompound having a carbon-carbon unsaturated bond is too low, the effectof enhancing the cycle characteristics of the battery may beinsufficient. In addition, the cyclic carbonate compound having acarbon-carbon unsaturated bond readily reacts with a positive electrodematerial in a charged state. Therefore, when the electrolytic solutioncontains the cyclic carbonate compound having a carbon-carbonunsaturated bond, the amount of gas generated during high-temperaturestorage may be increased or the battery characteristics may beinsufficient. However, the side reaction with the positive electrodematerial can be suppressed by simultaneously using Compound (1) orCompound (2) and/or Compound (3). This can achieve both enhancement ofcycle characteristics and suppression of gas generation and is thereforeparticularly preferred. However, if the concentration of the cycliccarbonate compound having a carbon-carbon unsaturated bond is too high,the amount of gas generated during high-temperature storage may beincreased, or the discharge characteristics at low temperature may bedeteriorated. Therefore, the upper limit thereof is usually 8 wt % orless, preferably 4 wt % or less, and most preferably 3 wt % or less.

<Cyclic Carbonate Compound Having a Fluorine Atom>

The cyclic carbonate compound having a fluorine atom also forms a stableprotection film on the surface of a negative electrode and can therebyenhance the cycle characteristics of the battery.

Examples of the cyclic carbonate compound having a fluorine atom includefluoroethylene carbonate (4-fluoro-1,3-dioxolan-2-one),4,5-difluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one,4,4,5-trifluoro-1,3-dioxolan-2-one,4,4,5,5-tetrafluoro-1,3-dioxolan-2-one,4-fluoro-5-methyl-1,3-dioxolan-2-one,4-fluoro-4-methyl-1,3-dioxolan-2-one,4,5-difluoro-4-methyl-1,3-dioxolan-2-one,4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one, andtrifluoromethyl-1,3-dioxolan-2-one. Among them, fluoroethylenecarbonate, 4,5-difluoro-1,3-dioxolan-2-one, and4-fluoro-5-methyl-1,3-dioxolan-2-one are preferred from the viewpoint ofenhancement of the cycle characteristics.

These cyclic carbonate compounds having fluorine atoms may be used aloneor in a combination of two or more.

When the nonaqueous electrolytic solution contains the cyclic carbonatecompound having a fluorine atom, the ratio thereof in the nonaqueouselectrolytic solution is usually 0.01 wt % or more, preferably 0.1 wt %or more, more preferably 0.3 wt % or more, and most preferably 0.5 wt %or more. When the amount of the cyclic carbonate compound having afluorine atom is too low, the effect of enhancing the cyclecharacteristics of the battery may be insufficient. Furthermore, thecyclic carbonate compound having a fluorine atom contained in theelectrolytic solution may lead to an increase in the amount of gasgenerated during high-temperature storage or insufficient batterycharacteristics. However, the simultaneous use of Compound (1) orCompound (2) and/or Compound (3) can achieve both the enhancement of thecycle characteristics and the suppression of the gas generation at thesame time, and is therefore particularly preferred. However, when theamount of the cyclic carbonate compound having a fluorine atom is toohigh, the amount of gas generated during high-temperature storage may beincreased or discharge characteristics at low temperature may bedeteriorated. Therefore, the upper limit thereof is usually 20 wt % orless, preferably 5 wt % or less, and most preferably 3 wt % or less.

<Monofluorophosphate and Difluorophosphate>

The monofluorophosphate and the difluorophosphate also form stableprotection film on the surface of a negative electrode and therefore canenhance the cycle characteristics of the battery.

Counter cations of the monofluorophosphate and the difluorophosphate arenot particularly limited, and Examples thereof include lithium, sodium,potassium, magnesium, and calcium. Among them, lithium is preferred.

Examples of the monofluorophosphate and the difluorophosphate includelithium monofluorophosphate, sodium monofluorophosphate, potassiummonofluorophosphate, lithium difluorophosphate, sodiumdifluorophosphate, and potassium difluorophosphate. Lithiummonofluorophosphate and lithium difluorophosphate are preferred, andlithium difluorophosphate is more preferred.

These may be used alone or in a combination of two or more.

The monofluorophosphate and/or the difluorophosphate may be usedtogether with a cyclic carbonate compound having a carbon-carbonunsaturated bond or a cyclic carbonate compound having a fluorine atom,and from the viewpoint of enhancement of the cycle characteristics, itis preferably used in combination with vinylene carbonate, vinylethylene carbonate, or fluoroethylene carbonate.

When the nonaqueous electrolytic solution contains themonofluorophosphate and/or the difluorophosphate, the ratio thereof inthe nonaqueous electrolytic solution is usually 0.001 wt % or more,preferably 0.01 wt % or more, more preferably 0.1 wt % or more, and mostpreferably 0.2 wt % or more. When the amount of the monofluorophosphateand/or the difluorophosphate is too small, the effect of enhancing thecycle characteristics of a battery may be insufficient. The upper limitis usually 5 wt % or less, preferably 3 wt % or less, and morepreferably 2 wt % or less.

Furthermore, when the nonaqueous electrolytic solution contains both thecyclic carbonate compound having a carbon-carbon unsaturated bond andthe cyclic carbonate compound having a fluorine atom, the total amountthereof is usually 0.01 wt % or more, preferably 0.1 wt % or more, morepreferably 0.3 wt % or more, and most preferably 0.5 wt % or more andusually 20 wt % or less, preferably 10 wt % or less, more preferably 5wt % or less, and most preferably 3 wt % or less, because of the samereasons as for the upper limit and the lower limit of the content ofeach compound.

In addition, when the nonaqueous electrolytic solution contains thecyclic carbonate compound having a carbon-carbon unsaturated bond and/orthe cyclic carbonate compound having a fluorine atom and themonofluorophosphate and/or the difluorophosphate, the total amountthereof is usually 0.01 wt % or more, preferably 0.1 wt % or more, morepreferably 0.3 wt % or more, and most preferably 0.5 wt % or more andusually 20 wt % or less, preferably 10 wt % or less, more preferably 5wt % or less, and most preferably 3 wt % or less, because of the samereasons as for the upper limit and the lower limit of the content ofeach compound.

<Overcharge Protection Agent>

Examples of the overcharge protection agent include aromatic compoundssuch as biphenyl, alkyl biphenyls, e.g., 2-methyl-biphenyl, terphenyls,partially hydrogenated terphenyls, cyclopentylbenzene,cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane,trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane,trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene,diphenyl ethers, and dibenzofuran; partially fluorinated compounds ofthe above-mentioned aromatic compounds such as 2-fluorobiphenyl,3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl,o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; andfluorine-containing anisole compounds such as 2,4-difluoroanisole,2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole.

Among them, aromatic compounds such as biphenyl, alkyl biphenyls, e.g.,2-methyl-biphenyl, terphenyls, partially hydrogenated terphenyls,cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane,trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane,trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene,diphenyl ethers, and dibenzofuran; and partially fluorinated compoundsof the above-mentioned aromatic compounds such as 2-fluorobiphenyl,3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl,o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene are preferred.Partially hydrogenated terphenyls, cyclopentylbenzene,cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane,trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane,trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene,o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene are morepreferred, and partially hydrogenated terphenyls and cyclohexylbenzeneare particularly preferred.

The overcharge protection agents may be used alone or in a combinationof two or more.

When two or more overcharge protection agents are simultaneously used, acombination of a partially hydrogenated terphenyl or cyclohexylbenzeneand t-butylbenzene or t-amylbenzene, and a combination of one selectedfrom aromatic compounds not containing oxygen such as biphenyl, alkylbiphenyls, terphenyls, partially hydrogenated terphenyls,cyclohexylbenzene, t-butylbenzene, and t-amylbenzene and one selectedfrom oxygen-containing aromatic compounds such as diphenyl ethers anddibenzofuran are preferred from the viewpoints of well-balancedovercharge protection characteristics and high-temperature storagecharacteristics.

The ratio of these overcharge protection agents in the nonaqueouselectrolytic solution is usually 0.1 wt % or more, preferably 0.2 wt %or more, more preferably 0.3 wt % or more, and most preferably 0.5 wt %or more, and the upper limit is usually 5 wt % or less, preferably 3 wt% or less, and most preferably 2 wt % or less. In a lower concentrationthan the lower limit, a desired effect of the overcharge protectionagent may be hardly exhibited. Conversely, the concentration of theovercharge protection agent is too high, the battery characteristicssuch as high-temperature storage characteristics tend to bedeteriorated.

<Other Auxiliaries>

Other auxiliaries are not particularly limited, and examples thereof areas follows:

carbonate compounds such as erythritan carbonate, spiro-bis-dimethylenecarbonate, and methoxyethyl-methyl carbonate;

carboxylic anhydrides such as succinic anhydride, glutaric anhydride,maleic anhydride, itaconic anhydride, citraconic anhydride, glutaconicanhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride,cyclopentanetetracarboxylic dianhydride, and phenylsuccinic anhydride;

dicarboxylic acid diester compounds such as dimethyl succinate, diethylsuccinate, diallyl succinate, dimethyl maleate, diethyl maleate, diallylmaleate, dipropyl maleate, dibutyl maleate, bis(trifluoromethyl)maleate,bis(pentafluoroethyl)maleate, and bis(2,2,2-trifluoroethyl)maleate;

spiro compounds such as 2,4,8,10-tetraoxaspiro[5.5]undecane and3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane;

sulfur-containing compounds such as ethylene sulfite, propylene sulfite,1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butenesultone, methyl methane sulfonate, ethyl methane sulfonate,methyl-methoxymethane sulfonate, methyl-2-methoxyethane sulfonate,busulfan, diethylene glycol dimethane sulfonate, 1,2-ethane diolbis(2,2,2-trifluoroethane sulfonate), 1,4-butane diolbis(2,2,2-trifluoroethane sulfonate), sulfolane, sulfolane, dimethylsulfone, diphenyl sulfone, N,N-dimethyl methanesulfonamide, andN,N-diethyl methanesulfonamide;

nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone,1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,1,3-dimethyl-2-imidazolidinone, and N-methyl succinimide;

hydrocarbon compounds such as heptane, octane, nonane, decane,cycloheptane, methylcyclohexane, ethylcyclohexane, propylcyclohexane,n-butylcyclohexane, t-butylcyclohexane, and dicyclohexyl;

fluorinated benzenes and fluorinated toluenes such as fluorobenzene,difluorobenzene, hexafluorobenzene, and benzotrifluororide; and

nitrile compounds such as acetonitrile, propionitrile, butyronitrile,malononitrile, succinonitrile, glutaronitrile, and adiponitrile.

These compounds may be used alone or in a combination of two or more.

The ratio of these auxiliaries in the nonaqueous electrolytic solutionis not particularly limited in order to exhibit the effect of thepresent invention, but is usually 0.01 wt % or more, preferably 0.1 wt %or more, and more preferably 0.2 wt % or more. The upper limit isusually 10 wt % or less, preferably 5 wt % or less, more preferably 3 wt% or less, and most preferably 1 wt % or less. These auxiliaries canenhance capacity-maintaining characteristics and cycle characteristicsafter high-temperature storage, but in a lower concentration than thelower limit, the effects of the auxiliaries may be hardly exhibited. Theconcentration is too high, battery characteristics such as high-loaddischarge characteristics may be deteriorated.

The above-mentioned cyclic carbonate compounds having carbon-carbonunsaturated bonds, cyclic carbonate compounds having fluorine atoms,monofluorophosphates, and difluorophosphates, overcharge protectionagents, and other auxiliaries may be used in any combination.

{Preparation of Nonaqueous Electrolytic Solution}

The nonaqueous electrolytic solution according to the present inventioncan be prepared by dissolving in a nonaqueous solvent an electrolyte,Compound (1) or Compound (2) and/or Compound (3), and other compoundsthat are blended according to need. In the preparation of the nonaqueouselectrolytic solution, each raw material is preferably dehydrated inadvance for reducing the amount of water when it is formed into anelectrolytic solution and is preferably dehydrated so that the watercontent is usually 50 ppm or less, preferably 30 ppm or less, and mostpreferably 10 ppm or less. Furthermore, after the preparation of theelectrolytic solution, dehydration and deacidification treatment may beperformed.

The nonaqueous electrolytic solution of the present invention issuitable for using as an electrolytic solution of nonaqueous electrolytebatteries, in particular, secondary batteries, that is, nonaqueouselectrolyte secondary batteries, for example, lithium secondarybatteries.

[Nonaqueous Electrolyte Battery]

The nonaqueous electrolyte battery of the present invention includesnegative and positive electrodes that can absorb and desorb lithium ionsand a nonaqueous electrolytic solution and is characterized in that thenonaqueous electrolytic solution is the above-described nonaqueouselectrolytic solution of the present invention.

As described above, since the nonaqueous electrolytic solution of thepresent invention is suitable for using as an electrolytic solution ofnonaqueous electrolyte batteries, in particular, secondary batteries,that is, nonaqueous electrolyte secondary batteries, for example,lithium secondary batteries, a nonaqueous electrolyte secondary batteryincluding the nonaqueous electrolytic solution of the present inventionwill be described below.

<Battery Configuration>

The nonaqueous electrolyte secondary battery according to the presentinvention is a nonaqueous electrolyte battery including negative andpositive electrodes that can absorb and desorb lithium ions and anonaqueous electrolytic solution, as in conventionally known nonaqueouselectrolyte secondary batteries, excluding using the above-mentionedelectrolytic solution of the present invention, and is usually producedby placing a porous film impregnated with the nonaqueous electrolyticsolution according to the present invention between the positiveelectrode and the negative electrode in a case. Therefore, the shape ofthe secondary battery according to the present invention is notparticularly limited and may be any of, for example, cylindrical-type,rectangular-type, laminated-type, coin-type, or large-type.

<Negative Electrode Active Material>

Examples of the negative electrode active material used includecarbonaceous materials and metal compounds that can absorb and desorblithium, lithium metals, and lithium alloys. These negative electrodeactive materials may be used alone or in a combination of two or more.Among them, the carbonaceous materials and metal compounds that canabsorb and desorb lithium are preferred.

Among the carbonaceous materials, graphite and graphite whose surface iscovered with higher amorphous carbon compared with graphite areparticularly preferred.

The graphite has a d value (interlayer distance) of the lattice plane(002 plane) of preferably 0.335 to 0.338 nm, more preferably 0.335 to0.337 nm, when determined from X-ray diffraction according to theGakushin-method. The crystallite size (Lc) determined from X-raydiffraction according to the Gakushin-method is usually 30 nm or more,preferably 50 nm or more, and most preferably 100 nm or more. The ashcontent is usually 1 wt % or less, preferably 0.5 wt % or less, and mostpreferably 0.1 wt % or less.

The graphite whose surface is covered with amorphous carbon preferablyincludes a core material of graphite having a d value of the latticeplane (0002 plane) of 0.335 to 0.338 nm, determined from X-raydiffraction, and a carbonaceous material adhering on the surface of thecore material and having a d value of the lattice plane (0002 plane)larger than that of the core material, determined from X-raydiffraction. The weight ratio of the core material and the carbonaceousmaterial having a d value of the lattice plane (0002 plane) larger thanthat of the core material, determined by X-ray diffraction, is 99/1 to80/20. By using this, a negative electrode that has a large capacity andhardly reacts with an electrolytic solution can be produced.

The particle diameter of the carbonaceous material is, as a mediandiameter measured by a laser diffraction scattering method, usually 1 μmor more, preferably 3 μm or more, more preferably 5 μm or more, and mostpreferably 7 μm or more and usually 100 μm or less, preferably 50 μm orless, more preferably 40 μm or less, and most preferably 30 μm or less.

The specific surface area of the carbonaceous material measured by a BETmethod is usually 0.3 m²/g or more, preferably 0.5 m²/g or more, morepreferably 0.7 m²/g or more, and most preferably 0.8 m²/g or more andusually 25.0 m²/g or less, preferably 20.0 m²/g or less, more preferably15.0 m²/g or less, and most preferably 10.0 m²/g or less.

When the carbonaceous material is analyzed by Raman spectrum using argonion laser light for the peak intensity I_(A) of a peak P_(A) in therange of 1570 to 1620 cm⁻¹ and the peak intensity I_(B) of a peak P_(B)in the range of 1300 to 1400 cm⁻¹, the ratio of I_(B) to I_(A)representing an R value (=I_(B)/I_(A)) is preferably in a range of 0.01to 0.7. In addition, the half width of a peak in the range of 1570 to1620 cm⁻¹ is preferably 26 cm⁻¹ or less and most preferably 25 cm⁻¹ orless.

Examples of the metal compound that can absorb and desorb lithiuminclude compounds containing metals such as Ag, Zn, Al, Ga, In, Si, Ge,Sn, Pb, P, Sb, Bi, Cu, Ni, Sr, or Ba. These metals are used as a simplesubstance, as an oxide, or as an alloy with lithium. In the presentinvention, those containing elements selected from Si, Sn, Ge, and Alare preferred, and oxides or lithium alloys of metals selected from Si,Sn, and Al are more preferred. These may be in a powder state or in athin-film state and may be crystalline or amorphous.

The metal compounds that can absorb and desorb lithium, the oxidesthereof, and the alloys thereof with lithium generally have a capacityper unit weight larger than those of carbonaceous materials typicallyrepresented by graphite and therefore are suitable for lithium secondarybatteries that are required to have a higher energy density.

The average particle diameters of the metal compounds that can absorband desorb lithium, the oxides thereof, and the alloys thereof withlithium are not particularly limited for exhibiting the effect of thepresent invention and are usually 50 μm or less, preferably 20 μm orless, and most preferably 10 μl or less and usually 0.1 μm or more,preferably 1 μm or more, and most preferably 2 μm or more. When theaverage particle diameter is larger than this upper limit, the expansionof the electrode may become large, and thereby the cycle characteristicsmay be deteriorated. When lower than this lower limit, the currentcollection may become difficult, and thereby the capacity may beinsufficient.

<Positive Electrode Active Material>

The positive electrode active material is not particularly limited aslong as it can absorb and desorb lithium ions. Preferred are thosecontaining lithium and at least one transition metal. Examples thereofinclude lithium transition metal complex oxides and lithium-containingtransition metal phosphate compounds.

The transition metal of the lithium transition metal complex oxide ispreferably, for example, V, Ti, Cr, Mn, Fe, Co, Ni, or Cu. Specificexamples thereof include lithium-cobalt complex oxides such as LiCoO₂,lithium-nickel complex oxides such as LiNiO₂, lithium-manganese complexoxides such as LiMnO₂, LiMn₂O₄, and Li₂MnO₃, and those in which thetransition metal atoms as the main components of these lithiumtransition metal complex oxides are partially substituted by anothermetal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, orSi. Examples of the substituted lithium transition metal complex oxideinclude LiNi_(0.5)Mn_(0.5)O₂, LiNi_(0.85)Co_(0.10)Al_(0.05)O₂,LiNi_(0.33)Co_(0.33)Mn_(0.33)O₂, LiMn_(1.8)Al_(0.2)O₄, andLiMn_(1.5)Ni_(0.5)O₄.

The transition metal of the lithium-containing transition metalphosphate compound is preferably, for example, V, Ti, Cr, Mn, Fe, Co,Ni, or Cu. Examples thereof include iron phosphates such as LiFePO₄,Li₃Fe₂ (PO₄)₃, and LiFeP₂O₇, cobalt phosphates such as LiCoPO₄, andthose in which the transition metal atoms as the main components ofthese lithium transition metal phosphate compounds are partiallysubstituted by another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni,Cu, Zn, Mg, Ga, Zr, Nb, or Si.

These positive electrode active materials may be used alone or in acombination.

Furthermore, a material having a composition different from that of themain material constituting the positive electrode active material mayadhere on the surface of the positive electrode active material.Examples of the material adhering on the surface include oxides such asaluminum oxide, silicon oxide, titanium oxide, zirconium oxide,magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuthoxide; sulfates such as lithium sulfate, sodium sulfate, potassiumsulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; andcarbonates such as lithium carbonate, calcium carbonate, and magnesiumcarbonate. These materials also may be used alone or in a combination.

The amount of the material adhering on the surface is not particularlylimited for exhibiting the effect of the present invention, but thelower limit is, as the mass with respect to the positive electrodeactive material, preferably 0.1 ppm or more, more preferably 1 ppm ormore, and further preferably 10 ppm or more, and the upper limit ispreferably 20% or less, more preferably 10% or less, and furtherpreferably 5% or less. The material adhering on the surface can suppressoxidation reaction of the nonaqueous electrolytic solution on thesurface of the positive electrode active material, resulting inenhancement in the battery lifetime. However, when the amount of theadhesion is too small, the effect may be insufficient, and when toolarge, incoming and outgoing motions of lithium ions are inhibited andthereby the resistance may be increased.

<Adhesive, Thickener, and Electrically Conductive Material>

Any adhesive for binding an active material can be used as long as it isstable for the solvent used in the production of the electrode and theelectrolytic solution. Examples of the adhesive include fluorine resinssuch as poly(vinylidene fluoride) and polytetrafluoroethylene;polyolefins such as polyethylene and polypropylene; polymers havingunsaturated bonds and copolymers thereof, such as styrene-butadienerubber, isoprene rubber, and butadiene rubber; and acrylic acid polymersand copolymers thereof, such as ethylene-acrylic acid copolymers andethylene-methacrylic acid copolymers. These may be used alone or in acombination.

The electrodes may further contain, for example, a thickener, anelectrically conductive material, or a filler in order to enhancemechanical strength or electrical conductivity.

Examples of the thickener include carboxylmethyl cellulose, methylcellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol,oxidized starch, phosphorylated starch, and casein. These may be usedalone or in a combination.

Examples of the electrically conductive material include metal materialssuch as copper and nickel and carbon materials such as graphite andcarbon black. These may be used alone or in a combination.

<Production of Electrode>

The electrodes may be produced by a common method. For example, anelectrode can be formed by adding an adhesive, a thickener, anelectrically conductive material, a solvent, and other components to anegative or positive electrode active material, making the resultingmixture into slurry, applying the slurry to a current collector, anddrying and then pressing it.

In addition, a sheet electrode can be formed by directly forming a rollof that prepared by adding an adhesive, an electrically conductivematerial, and other components to an active material; a pellet electrodecan be formed by compression molding; or a thin film of an electrodematerial can be formed on a current collector by a method such asdeposition, sputtering, or plating.

When the negative electrode active material is graphite, the densityafter the drying and pressing of the negative electrode active materiallayer is usually 1.45 g/cm³ or more, preferably 1.55 g/cm³ or more, morepreferably 1.60 g/cm³ or more, and most preferably 1.65 g/cm³ or more.

The density after the drying and pressing of the positive electrodeactive material layer is usually 2.0 g/cm³ or more, preferably 2.5 g/cm³or more, and more preferably 3.0 g/cm³ or more.

<Current Collector>

Many types of current collectors can be used, and a metal or an alloy isgenerally used. Examples of the current collector of the negativeelectrode include copper, nickel, and stainless steel, and copper ispreferred. Examples of the current collector of the positive electrodeinclude metals such as aluminum, titanium, and tantalum and alloysthereof, and aluminum and alloys thereof are preferred.

<Separator and Outer Package>

A porous film (separator) is disposed between the positive electrode andthe negative electrode for preventing short circuit. In this case, theporous film is impregnated with the electrolytic solution. The materialand the shape of the porous film are not particularly limited as long asthey are stable to the electrolytic solution and excellent inliquid-holding properties. Preferred examples thereof include poroussheets made of a polyolefin such as polyethylene or polypropylene andnonwoven cloths.

Any material can be used for the outer package of the battery accordingto the present invention, and examples thereof include iron plated withnickel, stainless steel, aluminum and alloys thereof, nickel, titanium,and laminated films.

The operating voltage range of the above-mentioned nonaqueouselectrolyte secondary batteries of the present invention is generally 2to 6 V.

EXAMPLES

The present invention will be further specifically described withExamples and Comparative Examples below, but is not limited to theseExamples, within the scope not departing from the gist of the presentinvention.

In addition, each method for evaluating the batteries obtained in thefollowing Examples and Comparative Examples is shown below.

[Capacity Evaluation]

A nonaqueous electrolyte secondary battery disposed between glass platesin order to enhance the adhesion between electrodes was charged to 4.2 Vwith a constant current equivalent to 0.2 C at 25° C. and thendischarged to 3 V at a constant current of 0.2 C. This was performedthree times to stabilize the battery. In the fourth cycle, the batterywas charged to 4.2 V with a constant current of 0.5 C, then charged to acurrent value of 0.05 C at a constant voltage of 4.2 V, and thendischarged to 3 V at a constant current of 0.2 C, and the initialdischarge capacity was determined.

The term 1 C herein represents a current value when the referencecapacity of a battery is discharged for one hour, and 0.2 C is thecurrent value of one-fifth thereof.

[Evaluation of Continuous Charge Characteristics]

The battery after the capacity evaluation test was immersed in anethanol bath for measuring the volume. Then, the battery was chargedtill 4.25 V with a constant current of 0.5 C at 60° C. and thencontinuously charged at a constant voltage for one week.

The battery was cooled and then immersed in an ethanol bath formeasuring the volume. The amount of gas generated was determined from achange in the volume before and after the continuous charging.

After the measurement of the amount of the generated gas, the batterywas discharged to 3 V at a constant current of 0.2 C at 25° C. formeasuring the remaining capacity after the continuous charge test. Theratio of the discharge capacity after the continuous charge test to theinitial discharge capacity was determined and was defined as theremaining capacity (%) after continuous charging.

[Evaluation of High-Temperature Storage Characteristics]

The battery after the capacity evaluation test was charged to 4.2 V witha constant current of 0.5 C at 25° C., then charged to a current valueof 0.05 C at the constant voltage of 4.2 V, and then stored at 85° C.for one day. Subsequently, the battery was discharged to 3 V at aconstant current of 0.2 C, and the remaining capacity after thehigh-temperature storage test was measured. The ratio of the dischargecapacity after the storage test to the initial discharge capacity wasdetermined and was defined as the remaining capacity (%) afterhigh-temperature storage.

[Evaluation of Battery Characteristics after Cycle Test]

The battery after the capacity evaluation test was charged to 4.2 V witha constant current of 0.5 C at 45° C., then charged to a current valueof 0.05 C at the constant voltage of 4.2 V, and then discharged to 3 Vat a constant current of 10. This cycle was repeated for 300 cycles as acycle test. Subsequently, the battery was charged to 4.2 V with aconstant current of 0.5 C at 25° C., then charged to a current value of0.05 C at the constant voltage of 4.2 V, and then discharged to 3 V at aconstant current of 1 C. Then, 1 C discharge capacity after the cycletest was measured.

The ratio of the 10 discharge capacity after the cycle test to theinitial discharge capacity was determined and was defined as 10discharge capacity (%) after the cycle test.

Example 1 Production of Negative Electrode

Ninety-four parts by weight of natural graphite powder and 6 parts byweight of poly(vinylidene fluoride) were mixed, wherein in the naturalgraphite powder had a d value of a lattice plane (002 plane) by X-raydiffraction of 0.336 nm, a crystallite size (Lc) of 652 nm., an ashcontent of 0.07 wt %, a median diameter by a laser diffractionscattering method of 12 μm, a specific surface area by a BET method of7.5 m²/g, an R value (=I_(B)/I_(A)) determined by Raman spectrumanalysis using argon ion laser light of 0.12, and a half width of a peakin the range of 1570 to 1620 cm⁻¹ of 19.9 cm⁻¹. Then,N-methyl-2-pyrrolidone was added thereto to form slurry. This slurry wasuniformly applied to one face of a copper foil having a thickness of 12μm and was dried. Then, the foil applied with the slurry was pressed toform a negative electrode such that the density of the negativeelectrode active material layer was 1.67 g/cm³.

<Production of Positive Electrode>

Ninety parts by weight of LiCoO₂, 4 parts by weight of carbon black, and6 parts by weight of poly(vinylidene fluoride) (manufactured by KurehaCorporation, trade name: “KF-1000”) were mixed, andN-methyl-2-pyrrolidone was added thereto to form slurry. This slurry wasuniformly applied to both faces of an aluminum foil having a thicknessof 15 μm and was dried. Then, the foil applied with the slurry waspressed to form a positive electrode such that the density of thepositive electrode active material layer was 3.2 g/cm³.

<Preparation of Electrolytic Solution>

Triethyl phosphonoformate was mixed with a mixture of ethylenecarbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio:2:3:3) under a dried argon atmosphere such that the content of thetriethyl phosphonoformate in the nonaqueous solvent was 0.5 vol %. Then,sufficiently dried LiPF₆ was dissolved therein at a ratio of 1.0 mol/Lto give an electrolytic solution.

<Production of Lithium Secondary Battery>

Using the above-mentioned positive electrode and negative electrode anda polyethylene separator, a battery element was produced by laminatingthe negative electrode, the separator, the positive electrode, theseparator, and the negative electrode in this order. This batteryelement was inserted into a bag composed of a laminated film of analuminum sheet (thickness: 40 μm) coated with resin layers on bothsides, while providing the terminals of the positive and negativeelectrodes in a protruding condition. Then, the electrolytic solutionwas poured into the bag, followed by vacuum sealing to produce asheet-type lithium secondary battery. Continuous charge characteristicsand high-temperature storage characteristics were evaluated. Theevaluation results are shown in Table 1.

Example 2

A sheet-type lithium secondary battery was produced as in Example 1except that triethyl phosphonoacetate was used instead of triethylphosphonoformate used in the preparation of the electrolytic solution ofExample 1, and continuous charge characteristics and high-temperaturestorage characteristics were evaluated. The evaluation results are shownin Table 1.

Example 3

A sheet-type lithium secondary battery was produced as in Example 1except that triethyl-3-phosphonopropionate was used instead of triethylphosphonoformate used in the preparation of the electrolytic solution ofExample 1, and continuous charge characteristics and high-temperaturestorage characteristics were evaluated. The evaluation results are shownin Table 1.

Example 4

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 0.8 vol % and dissolving sufficiently dried LiPF₆ therein at a ratioof 1.0 mol/L, and continuous charge characteristics and high-temperaturestorage characteristics were evaluated. The evaluation results are shownin Table 1.

Example 5

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoformate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoformate in the nonaqueous solventwas 0.5 vol % and further mixing vinylene carbonate with the resultingmixture such that the content of the vinylene carbonate in thenonaqueous electrolytic solution was 2 wt % and then dissolvingsufficiently dried LiPF₆ therein at a ratio of 1.0 mol/L, and continuouscharge characteristics and high-temperature storage characteristics wereevaluated. The evaluation results are shown in Table 1.

Example 6

A sheet-type lithium secondary battery was produced as in Example 5except that triethyl phosphonoacetate was used instead of triethylphosphonoformate used in the preparation of the electrolytic solution ofExample 5, and continuous charge characteristics and high-temperaturestorage characteristics were evaluated. The evaluation results are shownin Table 1.

Example 7

A sheet-type lithium secondary battery was produced as in Example 5except that triethyl-3-phosphonopropionate was used instead of triethylphosphonoformate used in the preparation of the electrolytic solution ofExample 5, and continuous charge characteristics and high-temperaturestorage characteristics were evaluated. The evaluation results are shownin Table 1.

Example 8

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 0.5 vol % and further mixing vinylene carbonate and fluoroethylenecarbonate with the resulting mixture such that the contents of thevinylene carbonate and the fluoroethylene carbonate in the nonaqueouselectrolytic solution were each 1 wt % and then dissolving sufficientlydried LiPF₆ therein at a ratio of 1.0 mol/L, and continuous chargecharacteristics and high-temperature storage characteristics wereevaluated. The evaluation results are shown in Table 1.

Example 9

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 1 vol % and further mixing vinylene carbonate with the resultingmixture such that the content of the vinylene carbonate in thenonaqueous solvent was 2 wt % and then dissolving sufficiently driedLiPF₆ therein at a ratio of 1.0 mol/L, and continuous chargecharacteristics and high-temperature storage characteristics wereevaluated. The evaluation results are shown in Table 1.

Example 10

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 2 vol % and further mixing vinylene carbonate with the resultingmixture such that the content of the vinylene carbonate in thenonaqueous electrolytic solution was 2 wt % and then dissolvingsufficiently dried LiPF₆ therein at a ratio of 1.0 mol/L, and continuouscharge characteristics and high-temperature storage characteristics wereevaluated. The evaluation results are shown in Table 1.

Example 11

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 2 vol % and further mixing lithium difluorophosphate with theresulting mixture such that the content of the lithium difluorophosphatein the nonaqueous electrolytic solution was 0.5 wt % and then dissolvingsufficiently dried LiPF₆ therein at a ratio of 1.0 mol/L, and continuouscharge characteristics and high-temperature storage characteristics wereevaluated. The evaluation results are shown in Table 1.

Comparative Example 1

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by dissolvingsufficiently dried LiPF₆ in a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) at aratio of 1.0 mol/L, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The evaluationresults are shown in Table 1.

Comparative Example 2

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 2 vol % and then dissolving sufficiently dried LiPF₆ therein at aratio of 1.0 mol/L, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The evaluationresults are shown in Table 1.

Comparative Example 3

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingvinylene carbonate with a mixture of ethylene carbonate, ethyl methylcarbonate, and dimethyl carbonate (volume ratio: 2:3:3) such that thecontent of the vinylene carbonate in the nonaqueous electrolyticsolution was 2 wt % and then dissolving sufficiently dried LiPF₆ thereinat a ratio of 1.0 mol/L, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The evaluationresults are shown in Table 1.

Comparative Example 4

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingvinylene carbonate and fluoroethylene carbonate with a mixture ofethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate(volume ratio: 2:3:3) such that the contents of the vinylene carbonateand the fluoroethylene carbonate in the nonaqueous electrolytic solutionwere each 1 wt % and then dissolving sufficiently dried LiPF₆ therein ata ratio of 1.0 mol/L, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The evaluationresults are shown in Table 1.

Comparative Example 5

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingtriethyl phosphonoacetate with a mixture of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3) such thatthe content of the triethyl phosphonoacetate in the nonaqueous solventwas 5 vol % and further mixing vinylene carbonate with the resultingmixture such that the content of the vinylene carbonate in thenonaqueous electrolytic solution was 2 wt % and then dissolvingsufficiently dried LiPF₆ therein at a ratio of 1.0 mol/L, and continuouscharge characteristics and high-temperature storage characteristics wereevaluated. The evaluation results are shown in Table 1.

TABLE 1 Nonaqueous electrolytic solution composition Lithium RemainingVinylene Fluoroethylene difluoro- Amount of gas Remaining capacityCompound (1) carbonate carbonate phosphate generated after capacityafter after high- Content*1 content*2 content*2 content*2 continuouscontinuous temperature Type (vol %) (wt %) (wt %) (wt %) charging (mL)charging (%) storage (%) Example 1 triethyl 0.5 — — — 0.27 99 87phosphonoformate Example 2 triethyl 0.5 — — — 0.20 98 87phosphonoacetate Example 3 triethyl-3-phosphono- 0.5 — — — 0.19 98 87propionate Example 4 triethyl 0.8 — — — 0.19 99 82 phosphonoacetateExample 5 triethyl 0.5 2 — — 0.51 99 88 phosphonoformate Example 6triethyl 0.5 2 — — 0.38 99 88 phosphonoacetate Example 7triethyl-3-phosphono- 0.5 2 — — 0.46 99 88 propionate Example 8 triethyl0.5 1 1 — 0.35 98 87 phosphonoacetate Example 9 triethyl 1 2 — — 0.35 9986 phosphonoacetate Example 10 triethyl 2 2 — — 0.37 99 84phosphonoacetate Example 11 triethyl 2 — — 0.5 0.28 99 85phosphonoacetate Comparative — — — — — 0.29 95 87 Example 1 Comparativetriethyl 2 — — — 0.30 96 76 Example 2 phosphonoacetate Comparative — — 2— — 0.53 97 88 Example 3 Comparative — — 1 1 — 0.51 98 87 Example 4Comparative triethyl 5 2 — — 0.54 98 72 Example 5 phosphonoacetate *1:content in nonaqueous solvent *2: content in nonaqueous electrolyticsolution

As obvious from Table 1, the batteries according to the presentinvention, using nonaqueous electrolytic solutions containing Compound(1) or Compound (1) and at least one compound selected from the groupconsisting of cyclic carbonate compounds having carbon-carbonunsaturated bonds, cyclic carbonate compounds having fluorine atoms,monofluorophosphates, and difluorophosphates, are excellent incontinuous charge characteristics and high-temperature storagecharacteristics.

Example 12

A sheet-type lithium secondary battery was produced as in Example 1except that the used electrolytic solution was prepared by mixingvinylene carbonate and triethyl-2-phosphonopropionate with a mixture ofethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate(volume ratio: 2:3:3) under a dried argon atmosphere such that thecontents of the vinylene carbonate and thetriethyl-2-phosphonopropionate in the nonaqueous electrolytic solutionwere 2 wt % and 0.5 wt %, respectively, and then dissolving sufficientlydried LiPF₆ therein at a ratio of 1.0 mol/L, and continuous chargecharacteristics and battery characteristics after a cycle test wereevaluated. The evaluation results are shown in Table 2.

Example 13

A sheet-type lithium secondary battery was produced as in Example 12except that triethyl-2-phosphonobutyrate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 14

A sheet-type lithium secondary battery was produced as in Example 12except that triethyl phosphonofluoroacetate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 15

A sheet-type lithium secondary battery was produced as in Example 12except that ethyl(diethylphosphinyl)acetate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 16

A sheet-type lithium secondary battery was produced as in Example 12except that the used electrolytic solution was prepared by mixingvinylene carbonate, fluoroethylene carbonate, andtriethyl-2-phosphonopropionate with a mixture of ethylene carbonate,ethyl methyl carbonate, and dimethyl carbonate (volume ratio: 2:3:3)such that the contents of the vinylene carbonate, fluoroethylenecarbonate, and the triethyl-2-phosphonopropionate in the nonaqueouselectrolytic solution were 1 wt %, 1 wt %, and 0.5 wt %, respectively,and then dissolving sufficiently dried LiPF₆ therein at a ratio of 1.0mol/L, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 17

A sheet-type lithium secondary battery was produced as in Example 12except that diethyl acetylphosphonate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 18

A sheet-type lithium secondary battery was produced as in Example 12except that dimethyl(2-oxopropyl)phosphonate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 19

A sheet-type lithium secondary battery was produced as in Example 12except that the used electrolytic solution was prepared by mixingvinylene carbonate and diethyl acetylphosphonate with a mixture ofethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate(volume ratio: 2:3:3) such that the contents of the vinylene carbonateand the diethyl acetylphosphonate in the nonaqueous electrolyticsolution were 2 wt % and 1 wt %, respectively, and then dissolvingsufficiently dried LiPF₆ therein at a ratio of 1.0 mol/L, and continuouscharge characteristics and battery characteristics after a cycle testwere evaluated. The evaluation results are shown in Table 2.

Example 20

A sheet-type lithium secondary battery was produced as in Example 12except that the used electrolytic was prepared by mixing vinylenecarbonate, fluoroethylene carbonate, and diethyl acetylphosphonate witha mixture of ethylene carbonate, ethyl methyl carbonate, and dimethylcarbonate (volume ratio: 2:3:3) such that the contents of the vinylenecarbonate, the fluoroethylene carbonate, and the diethylacetylphosphonate in the nonaqueous electrolytic solution were 1 wt %, 1wt %, and 0.5 wt %, respectively, and then dissolving sufficiently driedLiPF₆ therein at a ratio of 1.0 mol/L, and continuous chargecharacteristics and battery characteristics after a cycle test wereevaluated. The evaluation results are shown in Table 2.

Comparative Example 6

A sheet-type lithium secondary battery was produced as in Example 12except that the used electrolytic solution was prepared by mixingvinylene carbonate with a mixture of ethylene carbonate, ethyl methylcarbonate, and dimethyl carbonate (volume ratio: 2:3:3) such that thecontent of the vinylene carbonate in the nonaqueous electrolyticsolution was 2 wt % and then dissolving sufficiently dried LiPF₆ thereinat a ratio of 1.0 mol/L, and continuous charge characteristics andbattery characteristics after a cycle test were evaluated. Theevaluation results are shown in Table 2.

Comparative Example 7

A sheet-type lithium secondary battery was produced as in Example 12except that the used electrolytic solution was prepared by mixingvinylene carbonate and fluoroethylene carbonate with a mixture ofethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate(volume ratio: 2:3:3) such that the contents of the vinylene carbonateand the fluoroethylene carbonate in the nonaqueous electrolytic solutionwere each 1 wt % and then dissolving sufficiently dried LiPF₆ therein ata ratio of 1.0 mol/L, and continuous charge characteristics and batterycharacteristics after a cycle test were evaluated. The evaluationresults are shown in Table 2.

Comparative Example 8

A sheet-type lithium secondary battery was produced as in Example 12except that ethyl diethyl phosphinate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

Example 21

A sheet-type lithium secondary battery was produced as in Example 12except that triethyl phosphonoacetate was used instead oftriethyl-2-phosphonopropionate in the electrolytic solution of Example12, and continuous charge characteristics and battery characteristicsafter a cycle test were evaluated. The evaluation results are shown inTable 2.

TABLE 2 Nonaqueous electrolytic solution composition Vinylene Amount ofgas Remaining 1C capacity Compound (2) or Compound (3) carbonateFluoroethylene generated after capacity after after cycle Contentcontent carbonate continuous continuous test Type (wt %) (wt %) content(wt %) charging (mL) charging (%) (%) Example 12 triethyl-2-phosphono-0.5 2 — 0.35 98 70 propionate Example 13 triethyl-2-phosphono- 0.5 2 —0.36 98 65 butyrate Example 14 triethyl phosphono- 0.5 2 — 0.30 99 68fluoroacetate Example 15 ethyl(diethyl- 0.5 2 — 0.38 98 69phosphinyl)acetate Example 16 triethyl-2-phosphono- 0.5 1 1 0.34 98 72propionate Example 17 diethyl acetylphos- 0.5 2 — 0.38 99 73 phonateExample 18 dimethyl(2-oxo- 0.5 2 — 0.39 98 72 propyl)phosphonate Example19 diethyl acetyl- 1 2 — 0.37 98 73 phosphonate Example 20 diethylacetyl- 1 1 1 0.36 98 75 phosphonate Comparative — — 2 — 0.53 97 47Example 6 Comparative — — 1 1 0.51 98 58 Example 7 Comparative ethyldiethyl 0.5 2 — 0.53 98 50 Example 8 phosphinate Example 21 triethylphosphono- 0.5 2 — 0.38 99 61 acetate

As obvious from Table 2, the batteries according to the presentinvention, using nonaqueous electrolytic solutions containing Compound(2), Compound (3), or Compound (2) or (3) and at least one compoundselected from the group consisting of cyclic carbonate compounds havingcarbon-carbon unsaturated bonds, cyclic carbonate compounds havingfluorine atoms, monofluorophosphates, and difluorophosphates, are low ingas generation and excellent in battery characteristics.

The present invention has been described in detail with specificEmbodiments, but it is obvious to those skilled in the art that thepresent invention can be variously modified without departing from thegist and scope of the invention.

This application is based on Japanese Patent Application (PatentApplication No. 2007-70848) filed on Mar. 19, 2007, Japanese PatentApplication (Patent Application No. 2007-193525) filed on Jul. 25, 2007,and Japanese Patent Application (Patent Application No. 2007-235600)filed on Sep. 11, 2007, the entire contents of which are herebyincorporated by reference.

1: A nonaqueous electrolytic solution comprising: an electrolyte, anonaqueous solvent, and a compound represented by at least one formulaselected from the group consisting of Formula (2) and Formula (3),

wherein for Formula (2), R¹¹ to R¹⁴ each independently represent ahydrogen atom, a halogen atom, or a monovalent substituent having 1 to12 carbon atoms; R¹⁵ represents an alkyl group having 1 to 12 carbonatoms, optionally substituted by a halogen atom, an alkenyl group having2 to 12 carbon atoms, optionally substituted by a halogen atom, an arylgroup having 6 to 12 carbon atoms, optionally substituted by a halogenatom, or an aralkyl group having 7 to 12 carbon atoms, optionallysubstituted by a fluorine atom; and m is an integer of 0 to 6, and

wherein for Formula (3), R²¹ to R²⁴ each independently represent ahydrogen atom, a halogen atom, or a monovalent substituent having 1 to12 carbon atoms; R²⁵ represents an alkyl group having 1 to 12 carbonatoms, optionally substituted by a halogen atom, an alkenyl group having2 to 12 carbon atoms, optionally substituted by a halogen atom, an arylgroup having 6 to 12 carbon atoms, optionally substituted by a halogenatom, or an aralkyl group having 7 to 12 carbon atoms, optionallysubstituted by a halogen atom; and r is an integer of 0 to 6, providedthat when both R²¹ and R²² are alkoxy groups, r is an integer of 1 to 6,and at least one of R²³ and R²⁴ represent a group other than a hydrogenatom. 2: The nonaqueous electrolytic solution according to claim 1,wherein R¹¹ to R¹⁴ are each independently selected from the groupconsisting of a hydrogen atom, a fluorine atom, an alkyl group, analkenyl group, an aryl group, an aralkyl group, an alkoxyalkyl group,and a group represented by R^(a)—O— in which R^(a) represents an alkylgroup, an alkenyl group, an aryl group, an aralkyl group, or analkoxyalkyl group. 3: The nonaqueous electrolytic solution according toclaim 1, wherein R¹⁵ is selected from the group consisting of a methylgroup, an ethyl group, an n-propyl group, an i-propyl group, an n-butylgroup, an i-butyl group, a sec-butyl group, a tert-butyl group, a pentylgroup, a cyclopentyl group, a cyclohexyl group, a vinyl group, an allylgroup, a phenyl group, a tolyl group, a xylyl group, a benzyl group, aphenethyl group, a trifluoromethyl group, a trifluoroethyl group, apentafluoroethyl group, a 2-fluorovinyl group, a 3-fluoro-2-propenylgroup, a 2-fluorophenyl group, a 3-fluorophenyl group, a 4-fluorophenylgroup, a 2,4-difluorophenyl group, a 3,5-difluorophenyl group, a2-fluorobenzyl group, a 3-fluorobenzyl group, a 4-fluorobenzyl group, a2,4-difluorobenzyl group, and a 3,5-difluorobenzyl group. 4: Thenonaqueous electrolytic solution according to claim 1, wherein R²¹ toR²⁴ are each independently selected from the group consisting of ahydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an arylgroup, an aralkyl group, an alkoxyalkyl group, and a group representedby R^(b)—O— in which R^(b) represents an alkyl group, an alkenyl group,an aryl group, an aralkyl group, or an alkoxyalkyl group. 5: Thenonaqueous electrolytic solution according to claim 1, wherein R²⁵ isselected from the group consisting of a methyl group, an ethyl group, ann-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, asec-butyl group, a tert-butyl group, a pentyl group, a cyclopentylgroup, a cyclohexyl group, a vinyl group, an allyl group, a phenylgroup, a tolyl group, a xylyl group, a benzyl group, a phenethyl group,a trifluoromethyl group, a trifluoroethyl group, a pentafluoroethylgroup, a 2-fluorovinyl group, a 3-fluoro-2-propenyl group, a2-fluorophenyl group, a 3-fluorophenyl group, a 4-fluorophenyl group, a2,4-difluorophenyl group, a 3,5-difluorophenyl group, a 2-fluorobenzylgroup, a 3-fluorobenzyl group, a 4-fluorobenzyl group, a2,4-difluorobenzyl group, and a 3,5-difluorobenzyl group. 6: Thenonaqueous electrolytic solution according to claim 1, comprising 0.001to 10 wt % of the compound. 7: The nonaqueous electrolytic solutionaccording to claim 1, further comprising at least one compound selectedfrom the group consisting of a cyclic carbonate compound having acarbon-carbon unsaturated bond, a cyclic carbonate compound having afluorine atom, a monofluorophosphate, and a difluorophosphate. 8: Thenonaqueous electrolytic solution according to claim 1, furthercomprising at least one cyclic carbonate compound having a carbon-carbonunsaturated bond selected from the group consisting of vinylenecarbonate, vinyl ethylene carbonate, 4-methyl-4-vinyl ethylenecarbonate, and 4,5-divinyl ethylene carbonate. 9: The nonaqueouselectrolytic solution according to claim 8, comprising 0.01 to 8 wt % ofthe cyclic carbonate compound having a carbon-carbon unsaturated bond.10: The nonaqueous electrolytic solution according to claim 7,comprising at least one cyclic carbonate compound having a fluorine atomselected from the group consisting of fluoroethylene carbonate,4,5-difluoro-1,3-dioxolan-2-one, and4-fluoro-5-methyl-1,3-dioxolan-2-one. 11: The nonaqueous electrolyticsolution according to claim 7, comprising 0.01 to 20 wt % of the cycliccarbonate compound having a fluorine atom. 12: The nonaqueouselectrolytic solution according to claim 1, comprising the compoundrepresented by Formula (2) wherein m is 0 or
 1. 13: The nonaqueouselectrolytic solution according to claim 1, comprising the compoundrepresented by Formula (3) wherein r is 0 or
 1. 14: The nonaqueouselectrolytic solution according to claim 1, comprising 0.01 to 4 wt % ofthe compound. 15: The nonaqueous electrolytic solution according toclaim 1, comprising 0.1 to 0.8 wt % of the compound. 16: The nonaqueouselectrolytic solution according to claim 1, further comprising anovercharge protection agent. 17: The nonaqueous electrolytic solutionaccording to claim 16, comprising 0.1 to 5 wt % of the overchargeprotection agent. 18: The nonaqueous electrolytic solution according toclaim 1, wherein the compound is at least one selected from the groupconsisting of triethyl-2-phosphonopropionate,triethyl-2-phosphonobutyrate, triethyl phosphonofluoroacetate,ethyl(diethylphosphinyl)acetate, diethyl acetylphosphonate, anddimethyl(2-oxopropyl)phosphonate. 19: The nonaqueous electrolyticsolution according to claim 18, comprising 0.001 to 10 wt % of thecompound. 20: The nonaqueous electrolytic solution according to claim18, further comprising vinylene carbonate.